The subject of Mutagens comes up a lot and I have some thoughts on the topic that I figured would make for interesting discussion.
Duration
5: 1 min
9: 10 min
13: 1 hr
17: 1 hr
Onset:
5: End of next turn.
9: 1 min
13: 1 min
17: End of next turn
For Alchemists that take the Fast Onset feat at Level 6, the Level 5 and Level 17 Mutagens can be used easily as combat buffs while the Level 9 and Level 13 Mutagens are too punishing to activate mid-combat but have a long enough duration to pre-buff. However, due to the number of abilities in the game which take 1-10 minutes of rest to use, the shorter-duration buffs may not last more than 1-2 combats. For Alchemists who don't take Fast Onset, none of the Mutagens available take effect quickly enough to activate mid-combat, making the Level 5 Mutagen useful only for certain skill challenges while relegating the rest to pre-buff options.
Personally, I'm fine with either short duration buffs with no onset time or long-duration buffs with a longer onset time. I like the idea of Fast Onset, but it doesn't do much for the Level 9 and 13 Mutagens which would still require 2 rounds to activate.
Idea 1: Instead of varying Onset time by Item Level, give all Mutagens a 1 minute onset. To offset the longer onset time, increase the duration of the Level 5 Mutagens to 10 minutes so that the durations look like this:
Duration:
5: 10 min
9: 10 min
13: 1 hr
17: 1 hr
Finally, change the Fast Onset class feature to allow all Mutagens to take effect at the end of the turn the user drinks them. This allows the Alchemist to use Mutagens as a combat buff while still allowing them to have a slight drawback in activation time. However, since the Alchemist can spend their actions to allow an ally to drink the Mutagen, you can buff an ally before their turn starts!
Idea 2: Instead of varying the Duration by level, make all Mutagens last 10 minutes as a baseline with the option to spend a limited resource (such as Focus) to make them last 1 hour. This gives the Level 5 and Level 9 Mutagens some potential use as long-duration buffs and makes it easier for players to remember the duration of their Mutagen.
The PF1 Mutagen granted a bonus and a penalty to one ability score each, and as the Alchemist gained levels they gained access to Discoveries which increased their Mutagen's bonuses and allowed them to apply to more ability scores at a time (while also taking a penalty to more ability scores). The penalty received never increased, and there was an item which removed the penalties entirely when worn.
The PF2 Mutagen grants its bonuses and penalties to the rolls and stats that their associated ability scores affect rather than applying to the ability score itself, which is a welcome change for new players trying to figure out exactly what it applies to. However, the PF2 Mutagen is an Item Bonus. This means it doesn't stack with bonuses granted by other magic items. Among these, the most common conflicting items are Weapon and Armor Potency Runes, Handwraps of Mighty Fists, and skill-boosting magic items (just trust me, there's a ton - not willing to type that whole list again. In situations where you're already benefitting from the highest-available bonus at your level (such as a +2 Potency Rune at Level 10) the applicable Mutagen will only grant a +1 bonus, meaning the more you invest in these stats the less a Mutagen will help.
Furthermore, unlike in PF1 the Mutagen penalty increases at higher item levels, and unlike Item Bonuses there aren't any conflicting Item Penalties to match them. The only way to negate the Mutagen penalty is via a Level 20 class feat, and at that point they only grant bonuses on things you don't have the highest-available magic item for. However, what this does mean is that an Alchemist can prepare Mutagens for situations where they'd be forced to use weapons and skills they don't excel in, which would allow them (and party members) to contribute on skills they normally wouldn't be capable of. That said, this stacking issue limits the offensive uses of the Bestial and Quicksilver Mutagens to Unarmed and Bomber Alchemists only, outside of fringe cases where a character loses their weapon, Handwraps of Mighty Fists, or Spell Duelist's Wand. For fans of the PF1 Alchemist, this is a huge shift to a very popular build type towards support and skills rather than offense.
Idea 1: Give Mutagens their own Bonus and Penalty type and lower the bonus / penalty. Most long-duration buff spells grant somewhere between a +1 and a +4 already anyway, so the following chart could work:
5: +1/-1
9: +2/-2
13: +3/-3
17: +4/-4
This has a few immediate beneficial effects. First, new players are going to be confused if presented with large numbers that don't actually stack - this removes that issue. Second, this makes it so that Mutagens grant the same level of bonus and penalty at all times, rather than applying a minor bonus with a major penalty at later levels. The main issue with this idea is that it increases the cap that characters can reach on attack, damage, and skills above the current levels, which would require a ton of rebalancing and make the Alchemist too powerful at force multiplication.
Idea 2: Limit the Bonus and Penalty of each Mutagen to a +1/-1 and allow it to stack with other bonus types. This has the same benefits as Idea 1 above while also avoiding the major drawback, but it presents its own issue as the Mutagen would no longer be very useful as an option to support by filling in on situations where the party is lacking. Other Elixirs could be made to fill in the gaps left by removing higher-level Mutagens without changing page space too much, but it would still make Mutagens less interesting. Perhaps higher-level Mutagens could be given alternate effects to compensate, such as increased reach, flight, additional senses, etc.
For now, that's all I can write. I have more ideas that'll probably have to wait until Wednesday, but in the meantime if anyone has any thoughts or ideas to share then I'm all ears.
As for onset, I'd prefer if all mutagens regardless of level started at the beginning of the user's next turn (representing the time to "hulk out"), whereas Fast Onset would make it take effect immediately on the action where you drink it. That way Fast Onset is still useful, but not a basically mandatory feat tax for someone who wants to use mutagens.
I'd also be fine with Fast Onset being removed from the game and all mutagens just going off immediately.
The subject of Mutagens comes up a lot and I have some thoughts on the topic that I figured would make for interesting discussion.
** spoiler omitted **
** spoiler omitted **...
i'm going to 100% disagree on what you think is the most common +item bonus.
Handwraps, weapons, skills and etc, i'm not really concerned about, they are basically saving you gold: If you go for feral, the mutagen is basically a free handwrap, so you won't be buying one, so there won't be any conflict.
But you will ALWAYS wear magical armor (or bracers) and that always gives +item bonus to ALL saving throws.
So, the conflict that you will have always will be on the +item bonus on saving throws.
That's... not exactly a 100% disagreement. I listed the biggest conflictions in no particular order, and I specifically mentioned the Armor Potency Rune as an issue. It's absolutely the #1 conflicting Item bonus in the game, but it's not the only one that matters. If you feel like reading a lot, I've spoilered my thoughts below.
For the Quicksilver Mutagen, you aren't saving any gold - the Item bonus applies to attacks only, so you'll be left dealing low damage unless you invest in a Potency Rune, and at that point the Mutagen penalizes you more than it helps since the Quicksilver Mutagen penalty scales with the bonus. With their lower HP, casters are better off using the Spell Duelist's Wand than a Quicksilver Mutagen if they want to land ranged TAC spells reliably (such as Disintegrate and Polar Ray). The only times you'll see a benefit from the Quicksilver Mutagen on your attack rolls that's possibly worth taking the penalty are if you're a Bomber Alchemist or you're using a ranged weapon as a backup and don't have a good Potency Rune, making it very limited in scope.
As for the skill bonuses, every skill has at least one magic item that grants an Item Bonus on the skill, and if you want to be a specialist in any given skill you absolutely need those items. Pretty much every character is going to have at least one skill-boosting item, and every Mutagen conflicts with at least one skill if not more. That's absolutely a common occurance.