Three questions please.
1) If a PC and a Monster both readied actions. For example, "as soon as any other PC walked in a room". My think is whoever readied their action first? I think ready action expire at the beginning of the player's next round.
2) How detail does the trigger needs to be? I am looking for a RAW answer.
3) If I ready an action, can I decide not to take the action even if the triggering condition was met?
I would probably say whoever has the highest initiative modifier goes first, but I don't think there is a RAW answer.
There is no level of specificity noted. Just "under what conditions you take the action." I would say it has to be something observable to the character.
Yes, you can decline to take a readied action.
And you are correct, if the readied action doesn't go off by your next turn, you would need to ready again, or do something else.
1. I'm not sure I understand the question. When a creature readies an action, that trigger is set until the start of their next turn (assuming the trigger doesn't take place). If you have two creatures readied on the same trigger, they take place at the same initiative order. Of course, in the case of ties amongst readied actions, it'd be whoever had the higher initiative.
2. The rules don't necessarily say, but some in-book examples are "When X starts to cast a spell," "When X charges me," and so on. In short, this means that the examples need to be generalistic and simple (i.e. you shouldn't be able to plan around any contingency via metagaming knowledge), but can be specific in terms of who or what you're readying (such as noting that your trigger will only work for enemies and not allies, and that you want to take specific actions, such as using Cleave V.S. making a regular attack).
In this case, the example from #1 is too specific, as you aren't aware of other PCs. A more appropriate readied trigger would be "If an enemy walks inside the room," since you wouldn't know whether the target is an enemy or not until you see them.
3. You can choose not to, since the rules say you "may" take the readied action in response to a trigger, but if the rules said that you "must" or that you "do," then you wouldn't get a choice.
Of course, this can backfire even if you choose not to take it based on the trigger you present. For example, when a person starts to cast a spell, you must decide to take the readied action before you know what the spell is, because making a Spellcraft check only works as its being cast, whereas the readied action must take place when they start casting a spell (and not during the act of casting a spell). Then again, some GMs would allow the "When X is casting a spell" readied action, which can circumvent that issue.
In short, a properly-worded Readied Action can get more out of shorting your action economy.
In this case, the example from #1 is too specific, as you aren't aware of other PCs. A more appropriate readied trigger would be "If an enemy walks inside the room," since you wouldn't know whether the target is an enemy or not until you see them.
In the case of the PC readying the action "an ally" is basically synonymous with "any other PC," and for the monster "an enemy" is also basically synonymous with "any other PC."
Sure his wording could be better, but its not much of a change.
My thoughts below, please comment. Looks like some are suggesting that just plan whoever has the higher initiate.
"The ready action lets you prepare to take an action later, after your turn is over but before your next one has begun."
"Then, anytime before your next action, you may take the readied action in response to that condition."
So it seems ready action expire right before the player's term. So with conflicting readied actions, the players the has a readied action will go first. This does change during the round.
Player A - 22 initiative
Player B - 20 initiative
Monster A - 18 initiative
Player C - 16 initiative
Both Player A & Monster A ready an action with similar trigger. Ready is in place.
Player C triggered the condition. - Player A will go first.
Rd 1 - Player A - readied an action
Rd 1 - Monster A - readied an action
Rd 1 - Player C - trigger the readies. Player A will go before Monster A, then Monster A, then Player C.
Player B triggered the condition. - Monster A will go first.
Rd 1 - Player A - readied an action
Rd 1 - Monster A - readied an action
End of Rd 1, nothing was triggered, readied action is still in effect
Rd 2 - Player A - pervious readied action expired. New ready action is readied.
Rd 2 - Player B - trigger the readies. (This happened before Monster A's turn) since Player A's readied action just happened right before Player B at the beginning of round 2. This mean the ready action is after Monster A round 1 action. Monster A will go before Player A, then Player A, then Player B.
This will repeat for future rounds. Let's say Rd 3
Player C triggered the condition on his turn during Rd 3. - Player A will go first.
Rd 3 - Player A - readied an action (renew ready from Rd 2 that is expired)
Rd 3 - Monster A - readied an action (renew ready from Rd 2 that is expired)
Rd 3 - Player C - trigger the readies. Player A will go before Monster A, then Monster A, then Player C.
I don't see any basis for using "who readied their action first" as a guideline.
They take their actions at the same time. This is the same as if two different characters had rolled the same initiative. I would just use the same rule for the tie breaker, higher initiative modifier.
The rules don't say anything about Initiative, but in the case of multiple readied actions, it makes the most sense so as to determine a proper flow of events, since Initiative is a statistic that the game uses to determines who goes first in a given combat round, and a creature with higher Initiative Score may decide to let another creature take its action first.
So using initiative modifier, not rolled initiative for the round?
Initiative modifier would makes sense and it is easier and it is static.
Either one works.