As GM I would never accept a Ready reaction being used as a perfect dodge, no matter how plausible are the rules explanation! Because we don't even have something closer to this in all currently released book. And even if we have some day, this probably will be restricted to a Monster's reaction. I can't even possible imagine some Paizo designer doing such thing as a player option.
A reaction that prevents an attack or dmg needs some kind of check. This usually is represented by an AC bonus like happen to Nimble Dodge
or Crane Flutter or some kind of attacker choice like happens to Glimpse of Redemption or some forced misfortune check to attack roll but never a perfect dodge.
OK. Several different types of responses to this, so I am going to do it in separate posts to keep things straight.
From a rules perspective:
If they would prefer fail forward (disrupts are not total waste of an action), then C1 might take half damage if the attack hits as they get graced by C2. This would mean that C1 didn't wast 2 actions and a reaction, and C2 didn't waste their strike/spell.
This is fairly clearly a houserule. Nothing printed in the rules suggests that this is or even should be how Ready a Stride action works.
It is a fairly reasonable houserule though. If you put it into the homebrew forum it would probably get good reception.
If they would prefer it to just be a negate, the attack would just miss as C2 swings at the empty space. C1 effectively traded their turn to block 1 hit.
This isn't accounting for the rules regarding disrupting actions. "Various abilities and conditions, such as an Attack of Opportunity, can disrupt an action." And those are specified in the reaction - such as attack of opportunity and stand still that both specify exactly under what conditions they disrupt the triggering action.
But you seem to be duplicating the effects of disrupting an action - "When an action is disrupted, you still use the actions or reactions you committed and you still expend any costs, but the action’s effects don’t occur." - even though neither Ready or Stride say that they disrupt actions under any conditions.
Specifically, you are disrupting the attacker's Strike action. The costs are still paid in the form of both action cost and MAP progression, but the Strike has no effect mechanically - swinging at the air isn't a mechanical effect.
| 1 person marked this as a favorite. |
Balance:
If they would prefer it to just be a negate, the attack would just miss as C2 swings at the empty space. C1 effectively traded their turn to block 1 hit.
This is horribly overpowered. Even considering the action cost.
Ascalaphus called it MAP Baiting, and I think that is an appropriate term for it.
The problem is that it basically gives the character doing this an infinite AC. Yes, it takes their entire turn, but it also means that it doesn't matter what level the enemy is - they don't get to roll, so they can never hit.
It is also a full turn for turn trade. The character is spending their entire turn, but it negates the entire turn of the enemy that tries to attack them. That isn't a balanced trade. Quite often, trading one of the PCs actions for one of the enemy's actions is considered a trade very much in favor of the players.
The bigger problem that I see is when the entire party uses this tactic against an enemy that doesn't have any attacks other than melee.
Round 1
All PCs:
◆ Ranged Strike
◆◆ Ready Step triggered by "Enemy attacks me"
Enemy:
Since the PCs are all doing this it doesn't matter which one it attacks.
◆ Stride
◆ Strike
PC: ↺ Step, which both disrupts the attack and moves the character out of range of melee attacks.
◆ Stride/Step to get in melee range again.
Round 2
PCs not adjacent to enemy
◆ Ranged Strike
◆◆ Ready Step triggered by "Enemy attacks me"
PC adjacent to enemy
◆ Step
◆◆ Ready Step triggered by "Enemy attacks me"
Enemy:
Now in exactly the same position as in Round 1. It doesn't matter which PC it tries to attack, the results will be the same.
◆ Stride
◆ Strike
PC: ↺ Step, which both disrupts the attack and moves the character out of range of melee attacks.
◆ Stride/Step to get in melee range again.
--------
This is uninteresting and not actually fun, it gives the players a feeling of winning, but it is horribly frustrating to the GM. It is straight-up cheese and shouldn't be allowed.
Edit: It isn't even a full turn for turn trade. The player characters are still getting one effective action on their turn. Either Step to move out of melee range, or Ranged Strike if they don't start adjacent to the enemy. So it is actually a trade of 2 actions and a reaction for all 3 actions from the enemy.
Comparisons to other proposed options that are similar:
If they would prefer it to just be a negate, the attack would just miss as C2 swings at the empty space. C1 effectively traded their turn to block 1 hit.
Compared to 'movement reaction after the attack', the enemy's turn is like this:
◆ Stride
◆ Strike
PC ↺ Step/Stride away, but the attack still resolves normally.
◆ Stride to either follow first PC or to attack a different one.
The enemy still gets one action. It is trading 2 actions and a reaction from the PC for 2 actions from the enemy. Still a good trade in favor of the PCs, but it doesn't completely negate the enemy's entire turn. And since the enemy does still get to make one attack, it means that players can't be cheesing enemies way above their character level.
----------
Compared to 'movement triggered by enemy moving into melee range'.
◆ Stride
PC ↺ Stride away
◆ Stride to follow
◆ Strike
Very similar result as before. Player is trading 2 actions and their reaction for 2 actions from the enemy spent on Striding to get in and stay in melee range. But the enemy still has one action that they can use effectively.
There is also precedent that a moving target can be struck before they leave a square: Attack of Opportunity. So moving away from an enemy does not immediately put you out of range of a melee attack.
Ironically, in the situation where readying a Stride negates an attack, that movement would trigger an Attack of Opportunity, so still within range to be attacked. Ultimately, I don't see a justification to negate the original Strike.
| 2 people marked this as a favorite. |
While some are against this for balance reasons (although the 2-action + reaction cost, + possibility of it not being triggered really allay that concern for me), I thought of a fun interaction. If you designated 'I am targeted by a Strike' as your trigger then it is entirely reasonable for a feint to trigger your reaction. Feints in general are also a good argument that the beginning of a Strike (before it lands) is a plausible observable trigger.
Forewarning, I haven't played with anyone using these tactics as a player or GM, but it sounds fun to me!
|
While some are against this for balance reasons (although the 2-action + reaction cost, + possibility of it not being triggered really allay that concern for me), I thought of a fun interaction. If you designated 'I am targeted by a Strike' as your trigger then it is entirely reasonable for a feint to trigger your reaction. Feints in general are also a good argument that the beginning of a Strike (before it lands) is a plausible observable trigger.
Forewarning, I haven't played with anyone using these tactics as a player or GM, but it sounds fun to me!
Agreed, I had the same thought yesterday. It could add a whole new dimension to combat, giving more relevance to feinting.
Also, such a tactic is not without cost. Readying costs two actions and a reaction. The casting message version costs 2 actions, 2 reactions, and a focus point. In addition, after the first time, most enemies could get wise. They could then never prompt the ready.
In light of those things, it has a greater potential to increase the dynamics of combat than stagnate it.
I don't think anyone's counting the action costs correctly.
Here's what you accomplish with the Ready a Stride tactic if you allow it to waste a Strike:
Stride, Negate a Hit, Apply -4/-5 to any subsequent Strikes
Normally, you would spend 1 Action Stride/Step away from an enemy to waste 1 enemy Action.
However, for 1 more Action that you would have spent to Stride/Step and your Reaction, you get the benefit of a Redeemer reaction protecting yourself (which Glimpse of Redeption can't do) with a forced choice on the enemy to take the "ally is unharmed" option (which Glimpse of Redemption can't force).
If someone wants to house rule this, that's fine, but people shouldn't expect this to be how Ready (Stride if I'm attacked) to work.
| 1 person marked this as a favorite. |
Feints in general are also a good argument that the beginning of a Strike (before it lands) is a plausible observable trigger.
Triggering the reaction on the start of an attack, yes. Negating the attack by being able to move away from it before the attack lands, no. Feint doesn't indicate that.
Forewarning, I haven't played with anyone using these tactics as a player or GM, but it sounds fun to me!
How much fun would it be for you and 3 allies at level 9 to be going up against 8 level 4 enemies that do this tactic. Each of them makes a ranged attack, then readies an action to flee when any of you approach and try to attack? Especially considering that you won't get any experience for defeating them since they are CR-5 enemies.
|
|
| 1 person marked this as a favorite. |
How much fun would it be for you and 3 allies at level 9 to be going up against 8 level 4 enemies that do this tactic. Each of them makes a ranged attack, then readies an action to flee when any of you approach and try to attack? Especially considering that you won't get any experience for defeating them since they are CR-5 enemies.
For me? A lot. I enjoy combats that are deviations from the standard. There are several ways to combat that tactic. So many that it might not be as much of a challenge as you think.
For me? A lot. I enjoy combats that are deviations from the standard. There are several ways to combat that tactic. So many that it might not be as much of a challenge as you think.
Yes, for a player. Ranged attacks of your own, spells, ...
But how much fun would it be if your characters were only able to use melee attacks that never get to land?
Now extend that to the other side of the screen. Take a look at how many enemies you can no longer use because they get wrecked by this tactic.
| 1 person marked this as a favorite. |
I also find it interesting that everyone promoting allowing the 'perfect kiting' tactic is arguing it from a balance perspective. No one that I have noticed has addressed the game rules argument that unless a reaction says that it disrupts an action, then it doesn't. If the trigger for Ready is based on the start of an action, then the action completes fully.
Maybe I just missed seeing it in the thread though.
Ready by itself cannot disrupt anything. What you Ready might alter events.
E.g., Ready Trip vs. a movement trigger. A successful Trip will affect the targets ability to move. However, that example does not mean that every readied action disrupts its trigger.
Nothing in Stride indicates that it prevents a Strike from resolving as you leave a square. In fact, as pointed out earlier, Striding out of a square gives ample time for a Strike to complete by virtue of Attack of Opportunity existing.
Does the converse provide the same protections: I Ready to Strike if my target moves out of his space. Same situation, a character Strikes and a character Strides. Does the Stride negate the Strike? I say no.
I'd be fine with a GM ruling that the Strike does not happen. The enemy moves to Strike but then your reaction triggers and you Stride away, forcing the enemy to chase after and then Strike. But in that case, nothing different happened in the interaction between Stride and Strike that what currently exists in the rules.
By that logic readying a trip doesn't work because trip doesn't say "disrupt" so the person beign tripped would move where ever they want still.
Well, I mentioned before that movement is reacted to in 5 foot intervals. So if you ready an action to trip someone if they Stride away, and your trip is successful, then they only go 5 feet and fall prone in that space.
1) Readying an action (2 actions and a reaction) is useless because they cannot actually disrupt anything.
Curious how you justify reactions being useless if they don't disrupt anything.
I see a lot of reactions built in to the game already. And only a few of them even have an option to disrupt actions and the ones that I can think of require critical success in order to actually do it.
So that line of reasoning seems to be a false dichotomy.
Some useful actions I can think of that use Ready:
* Closing a door after an ally goes through it but before any of the enemies can.
* Using a weapon with reach and trip traits to trip an enemy as soon as they Stride within range.
* Using disarm as soon as an enemy comes within range. The full disarm effect isn't likely to happen, but the penalty would apply to the rest of their turn unless they use an action to remove it.
* Moving in tandem with another ally so that you are never more than 5 feet apart, even if the enemies are also using reactions. (I don't have a concrete scenario where this one would be useful though, so it is a bit weaker than the others)
* Casting a 1-action spell when an enemy moves to attack you or an ally. Needle of Vengeance works well for that.
| 1 person marked this as a favorite. |
Just because some reactions call out disrupting doesn't mean that this is the only way to change the effect of an action, although some seem to have made an exception for this wording when it comes to Strides. Why? Sure movement reactions are triggered per square, but why are you taking that as precedent for move related triggers when you won't for other triggers? Nimble dodge allows for a reaction triggered by being targeted by an observed Strike and can alter the course of that Strike (even making it do nothing if it causes it to miss!) without mentioning the magical "disrupt" word.
Disrupt entirely cancels and action, which is not what the suggested readied actions actually do.
For example, suppose a cowardly Archer shot a Barbarian and then readied an action to flee if they tried to cut them down. This Barbarian uses Sudden Charge to close and Strike, causing the Archer to flee. This is not a disruption of the Strike, and to show why the Barbarian will now use their own reaction: No Escape. The foe tries to avoid the attack but ends up still in reach, so the Strike continues.
The same thing happens if a foe readies a Step instead of a Stride to avoid an AoO but is targeted by a reach weapon, they were outplayed. If they had actually disrupted the triggering action then it'd be stopped regardless, instead they merely changed the situation and not enough to avoid their fate.
Another fun one is someone with 4th level Silence cast on them readying an action to Stride next to a caster that tries to cast a Spell. Obviously a lot of these tactics will be telegraphed by a character only taking 1 action on their turn, although I'll admit that against mindless enemies these tactics could be abusable. That's already the case with a lot of tactics however, and is kind of the fatal flaw of creatures like Golems and other constructs. Still, the idea of PCs straight up outmaneuvering all foes with these tactics strikes me as some white room stuff that wouldn't work in a real situation with terrain and surprises.
| 1 person marked this as a favorite. |
So you are saying readying to shut down an opponent by using trip is okay.
Why wouldn't it be? It's the same as Tripping normally.
The problematic angle in this whole scenario is trying to handwave yourself into being able to negate an enemy's actions for free.
I am saying that you cannot say attacks are exempt from distuptions when everything else can be disrupted by the right action.
But that's not correct. The only way you're going to disrupt an action is if you... Disrupt it.
Movement works slightly differently because the rules describe how Reactions interact with movement. But that also only applies to movement.
So you are saying readying to shut down an opponent by using trip is okay.
But readying to dodge one attack, is game breaking and should be impossible.
Because that is how Trip works and that is not how Stride works. You're giving Stride an ability it does not possess.
If C1 wanted to Trip C2 who was X distance away, C1 could have walked over there and Tripped C2 with similar results: C2 is prone and within reach of C1. Instead, they want to stay where they are and only Trip C2 if they come within reach. The advantage being positioning.
Whereas if C1 wants to Stride away from C2, they can do that. Or they can stay there so that their buddy can get the flank effect and Ready an action to Stride away and C2 would need to Stride after c1 to be in melee range. So the end result, whichever trigger they choose, should be the same result as using the action Stride: C2 has to spend an action to Stride after them. You're giving it Best-Option Glimpse of Redemption on Self power, which doesn't exist.
AoO is a non-standard reaction that only a few select classes get by default, you have to get a feat to use it if your class doesn't give it to you. Just like champions get ways to negate attacks and gain resistance without spending their turn readying it.
You're saying AOO isn't a fair example of why this tactic shouldn't work because only a few select classes can do it (and only one at 1st level), but in the same paragraph you're saying the tactic should work because it's a better version of a reaction only a single subclass of a single class gets except it costs 1 whole action to cast.
Can also compare it to Shield Block. For 1 action you gain the benefit of an infinite hardness Shield Block while still able to not waste a hand on a shield.
| 3 people marked this as a favorite. |
I read the discussion going back and forth, and in my opinion there's no solution.
The game rules are a simulation. And as such they can't properly reflect each and every case you can encounter.
To solve that, you have GM adjudication.
This scenario exists since 3rd edition and is criticized since then (it was way stronger in 3rd edition as there was only one move action back then).
Still, I have years of gaming in 3rd, 4th, PF1 and PF2 and I've never seen this generating as much heat than in this thread. I think GM adjudication works fine to prevent it since then.
Ultimately, my rules argument is that you cannot--with the Ready action--separate the components of a Strike (selecting the target, any flat checks for concealment, the attack roll, the comparing to AC, determining the degree of success, and rolling damage). For the purposes of observable events that are not game terms, it is all one event from start to finish.
Your trigger is "the goblin Strikes at me," and the Strike must resolve (hit or miss) in order to satisfy the trigger. There is no "the goblin targets me but has not yet landed the blow" as an observable trigger for Ready any more than, if you were Concealed, using "the goblin makes his flat check vs. concealment" as a trigger.
That's my rules argument.
The rules offer no time for when a reaction happens, except that reactions triggered by movement without leaving your square happen after moving. So strikes get a special pass and trigger before movement?
You have misread or are misapplying that rule. Here's the whole rule below. It's about Move trait actions triggering reactions, and I don't think it helps your case anyway:
Actions with the move trait can trigger reactions or free actions throughout the course of the distance traveled. Each time you exit a square (or move 5 feet if not using a grid) within a creature’s reach, your movement triggers those reactions and free actions (although no more than once per move action for a given reacting creature). If you use a move action but don’t move out of a square, the trigger instead happens at the end of that action or ability.
| 1 person marked this as a favorite. |
Btw in your example, we both agree that if someone readies an action to strike someone that is running away the attack may land (still have to roll). So why is the opposite a special case where the strike must hit (still have to roll) even if the person is 20+ feet away and behind a wall when the strike actually resolves?
Don't combine mechanics with narrative.
Also, you are still misunderstanding my ruling. The defender isn't 20+ feet away when the Strike resolves. They are still in that adjacent square. The reaction happens after the Strike since the reaction started after the Strike started.
It feels like you are thinking that all reactions are like old-school Magic: The Gathering 'interrupts' where a reaction will always happen in full before its triggering action. That isn't what the rules describe.
Or the "Nope!" card in Exploding Kittens. :D
It feels like you are thinking that all reactions are like old-school Magic: The Gathering 'interrupts' where a reaction will always happen in full before its triggering action. That isn't what the rules describe.
To preemptively back up this statement:
You can use free actions that have triggers and reactions only in response to certain events.
"In response to" generally means "after" - the action that you are responding to happens first.
This also lines up with the concept of disrupting actions. Reactions that disrupt the triggering action still happen after their trigger, but they cause the triggering action to have no effect. It is a limited-scope rewind of game mechanics time ordering. But reactions in general don't rewind game mechanics time and happen before their triggers.
| 1 person marked this as a favorite. |
[snip]
Enemy:
Now in exactly the same position as in Round 1. It doesn't matter which PC it tries to attack, the results will be the same.
◆ Stride
◆ Strike
PC: ↺ Step, which both disrupts the attack and moves the character out of range of melee attacks.
◆ Stride/Step to get in melee range again...
As the GM, if allowing this, it should only continue working on mindless enemies.
After a time or two of this, the melee-only brute wises up, strides to the readied PC and then Grapples or Trips. Since those are Skill checks, not attacks, they do not trigger the readied action. Once the PC is grabbed or prone, then the brute strikes. The PC's readied action is triggered but fails since the PC must either escape the grab or stand up from prone before striding or stepping.
It's not particularly hard to meet PC shenanigans with GM shenanigans.
| 1 person marked this as a favorite. |
But, but, but, the trigger is 'the enemy "attacks" me'. Those are all still attack actions......
|
|
| 2 people marked this as a favorite. |
As a GM, I require an in-game prompt. "Attack" is too broad. "Winds back to swing their sword" is acceptable. This specification limits the power of the reaction.
If Nimble dodge can be prompted and resolved before the attack is resolved, I don't see why a ready cannot do the same. It is not outside of precedent.
Is it powerful? Yes. Can it be done every turn?...technically..but an enemy can just counter that tactic by not being within reach of a melee PC. If the PC uses 2 actions to do the ready shenanigans, what are they going to do with their 3rd that is any concern?
All in all, I really don't think it will be as powerful in practice. Chances are, it will be a 1 or 2 time use in combat at most.
Goodness forbid players be encouraged to use good tactics. Ya'know, like we keep telling new players to 2e that they should do for the best 2e experience.
| 2 people marked this as a favorite. |
If Nimble dodge can be prompted and resolved before the attack is resolved, I don't see why a ready cannot do the same. It is not outside of precedent.
Nimble Dodge also doesn't disrupt the attack. The attack is still rolled and can still hit the defender using it.
Goodness forbid players be encouraged to use good tactics. Ya'know, like we keep telling new players to 2e that they should do for the best 2e experience.
We also recommend that new players run the rules as they are intended. I don't think it is intended for monsters with no damage dealing spells or ranged attacks to just be completely ineffective - but only against players that are 'clever' enough to find this particular loophole.
-------
*Player party all starts perfect reaction kiting*
Well, I guess I will just stand here and die then.
'I'm readying an attack and the trigger is someone readying an attack. Now I just have to hope someone doesn't ready vs my ready...'
'I'm readying an attack and the trigger is someone readying an attack. Now I just have to hope someone doesn't ready vs my ready...'
LOL.
But, obligatory 'you can't ready an action triggered by a purely mental action'.
| 1 person marked this as a favorite. |
'I'm readying an attack and the trigger is someone readying an attack. Now I just have to hope someone doesn't ready vs my ready...'LOL.
But, obligatory 'you can't ready an action triggered by a purely mental action'.
Sure but it's not listed as purely mental. For instance, other things with concentrate, like Verbal, have concentrate and involve non-mental actions: I can totally see readying to Stride or Strike involve bracing your feet or getting into a stance [not a Stance]. They never explain exactly what you're doing with those 2 Ready actions. IMO, it'd be weird if you can Ready when paralyzed. And as Paralyzed mentions, "actions that require only the use of your mind (as determined by the GM)" so it's up to the Dm to adjudicate what is or isn't purely mental actions.
|
|
| 1 person marked this as a favorite. |
If Nimble dodge can be prompted and resolved before the attack is resolved, I don't see why a ready cannot do the same. It is not outside of precedent.Nimble Dodge also doesn't disrupt the attack. The attack is still rolled and can still hit the defender using it.
What Nimble Dodge specifically does is irrelevant.
We also recommend that new players run the rules as they are intended. I don't think it is intended for monsters with no damage dealing spells or ranged attacks to just be completely ineffective - but only against players that are 'clever' enough to find this particular loophole.
I'm not overly convinced by what you think is intended, given that others think the opposite. It kinda makes either side a bit moot.
*Player party all starts perfect reaction kiting*Well, I guess I will just stand here and die then.
Good thing a Babau can cast darkness. It is really hard for anyone to ready an action against an action they can't see coming....did you not really think through that example?
But, but, but, the trigger is 'the enemy "attacks" me'. Those are all still attack actions......
Um... no. Disarm, Grapple, Shove, and Trip are Athletics Skill checks with the Attack Trait. They are not "attack actions."
|
Anything with the attack trait is an attack action. They are not attack rolls.But, but, but, the trigger is 'the enemy "attacks" me'. Those are all still attack actions......Um... no. Disarm, Grapple, Shove, and Trip are Athletics Skill checks with the Attack Trait. They are not "attack actions."
Correct, for reference the Attack Rules and the Attack Trait.
If someone wanted to REALLY be abusive and split hairs they'd need to get their GM to not only agree to this stuff but they would also need to phrase the Reaction with wording that notes something like "I Ready a Stride for when an Opponent who is threatening me is about to make and 'attack roll.'"
| 4 people marked this as a favorite. |
If Nimble dodge can be prompted and resolved before the attack is resolved, I don't see why a ready cannot do the same. It is not outside of precedent.
What Nimble Dodge specifically does is irrelevant.
Good to know.
Anything with the attack trait is an attack action. They are not attack rolls.But, but, but, the trigger is 'the enemy "attacks" me'. Those are all still attack actions......Um... no. Disarm, Grapple, Shove, and Trip are Athletics Skill checks with the Attack Trait. They are not "attack actions."
Well shioot. Tripped up again by rhetorical nuances.
We [my game group] have been under the impression that the first erratta regarding maneuvers (skill checks with the Attack trait) clarified that they are Skill Checks not Attacks.
Thanks for the correction!!
Anything with the attack trait is an attack action. They are not attack rolls.But, but, but, the trigger is 'the enemy "attacks" me'. Those are all still attack actions......Um... no. Disarm, Grapple, Shove, and Trip are Athletics Skill checks with the Attack Trait. They are not "attack actions."Correct, for reference the Attack Rules and the Attack Trait.
If someone wanted to REALLY be abusive and split hairs they'd need to get their GM to not only agree to this stuff but they would also need to phrase the Reaction with wording that notes something like "I Ready a Stride for when an Opponent who is threatening me is about to make and 'attack roll.'"
You could also do:
"When an enemy that I see draws a bow" (as in they are about to shoot an arrow)
"When an enemy that I see starts chanting a spell"
"When an enemy that I see starts to move their arm to attack"
etc.
Sure, I'd probably let a player Ready a Stride with all of those as a trigger, but in each of those cases I'd also rule the NPC doesn't spend actions or advance their MAP by shooting/casting/striking at empty air and can choose to do something else with all 3 of their actions.
| 2 people marked this as a favorite. |
Why? I ask rhetorically. Stride doesn't do anything to another character. Trip does do something to another character. And only on a successful skill check vs. a DC.
You can't have your cake and eat it too. Either the character strides away at the first sign of aggression so fast that there's no chance that enemy could hit them and so has time to recognize there is no valid target in their square or they start to leave when the act is so committed that it costs an action that they're there to risk getting hit.
EDIT: Also, if I had an NPC ready a Trip action against a player, it would be because I was trying to not steamroll the party with damage, so they'd be happy I wasted actions on that rather than two Strikes.
Reading through some of the comments I feel like I'm missing something: where in the rules does it say that a readied action needs to have a trigger that you can describe in character / notice in the game world? I know that's a thing for 5e, but in pf2 the ready rules simply say to set a trigger. Exact text is below:
"Ready (2 actions)
You prepare to use an action that will occur outside your turn. Choose a single action or free action you can use, and designate a trigger. Your turn then ends. If the trigger you designated occurs before the start of your next turn, you can use the chosen action as a reaction (provided you still meet the requirements to use it). You can’t Ready a free action that already has a trigger.
If you have a multiple attack penalty and your readied action is an attack action, your readied attack takes the multiple attack penalty you had at the time you used Ready. This is one of the few times the multiple attack penalty applies when it’s not your turn."
As far as I can tell this means that any trigger that other abilities are allowed to use should be available for the ready action as well, so other reactions gained from feats are great examples of possible triggers.
If I'm wrong I'd be happy to be pointed to the reference, but I've seen it said a couple times now that your character needs to be able to perceive the trigger in the world for it to work as if that's just common knowledge and I'm struggling to find that in the rules.
EDIT: Did some more digging and apparently it's in the GMG. I rescind my statement. Still kind of annoying that's not in the actual rules for Ready that players see though