I have a player who wants to try a multiple personality character, so one character who can switch between the classes...
His vision:
Let's say I "work with magic" I think it would be crazy awesome if my character was this weak jerk who manufactured rainbow colored potions (using elements I can get through adventures) and each colored potion would turn me into a different character class...but only for like, a period of a few rounds, or hours...
And each time I changed, ...it would be as if I had five distance personalities, that were locked away, so whenever I drank, let's say, a red, or "warrior" potion, i would grow a bunch of muscles, and ask what was going on...as if I had summoned something in my place.Any ideas that fit the rules, but keep this manageable and fair?
I'd recommend an alchemist or a druid. Alchemists have their mutagens and druids wildshape. What he's asking for sounds like he wants to be able to do everything whenever he needs/wants to. I can see this stepping on the toes of the rest of the party and pissing them off. Another option is just a whole lot of multiclassing. He could use buff potions to boost what he was doing at the moment.
I'd recommend an alchemist, eventually entering into the Master Chymist Prestige Class.
Switching outright between different classes would be extremely powerful, and more importantly could make others at the table resent the character; what's the point of being the party's scout when the alchemist can simply drink his rogue potion and do the job just as well? In some cases even better, since if the alchemist gets caught snooping on the monsters, he just drinks his fighter potion and stands his ground solo.
As everybody said, Alchemist seems right up this ally.
I would say that perhaps Synthesist Summoner, using spells to shift around Evolutions, could achieve similar effect,
but it doesn`t have the same chugging potions aspect that Alchemist has from the very start.
Going with Alchemist, I would be flexible in denoting different personalities that correspond to different mutagenic/extract states... The class as written basically has two, but you could expand it to when he jacks one stat / ditches another, a different personality comes out, for at least 6 personalities, and if you bring other extract effects into the mix (enlarge person, blur, etc) those could be even more.
This is the kind of idea that can be very game-disrupting to other players (aside from class balance issues), so I would caution him to not over-due it especially all at the start.