I want to be a Monster

[Tabris623]

So I am a part of a low power, horror campaign in pathfinder. I really enjoying myself so far but I am pretty sure this character is going to die horribly at some point in the near future. I have been looking at the gunslinger class but what I really want to make is some kind of crazy shape-shifting monster. This normally wouldn't be a problem but we are restricted to no splats and only human. I was wondering if there was a solid core way of getting Alter Self or something similar. We have been encountering crazy eldritch horrors and I really want to embrace that and turn it against the party's foes. Any suggestions would be great.

[Grod_The_Giant]

You want the Synthesist Summoner, if possible. They get to wear their eidolons like power armor- it's the best make-your-own-monster option in the game. You also probably want the 3.5/pf board- if you report your own post you can get it moved.

[Tabris623]

Thank you. This might not be allowed but it is a fantastic idea and it sounds awesome and fun to play.

[Grod_The_Giant]

What does "core" cover? You mentioned Gunslinger, which isn't in the PHB...

[Tabris623]

I never actually realized that (I usually use the pfsrd). All he said was no "splats" or 3.5 stuff. Tbh, I am not exactly sure what qualifies as splats in pf as this is not the system I normally play.

[Grod_The_Giant]

I'd guess just the PHB, but it's worth asking. (The pfsrd specifies where things come from on the bottom of an article)

[Gallowglass]

If synthesist summoner doesn't fly, try the alchemist beastmorph archtype

[Milo v3]

I never actually realized that (I usually use the pfsrd). All he said was no "splats" or 3.5 stuff. Tbh, I am not exactly sure what qualifies as splats in pf as this is not the system I normally play.
There are two meaning of "Core" in the Pathfinder community; the true meaning is "Just the core rulebook", while some GM's mean "Just the books in the Roleplaying Game-line, and no Player Companions or Campaign Setting splats". You should probably find out which your GM means, since if it's the first one then you likely wont have much luck with your concept.

Either way, I think you should look at the PRD rather than PFSRD, since most of the PFSRD isn't Core by either of the two definitions (with most of it being from Player Companions and Third-Party products because of the sheer amount of content that exists). PRD has content seperated by what book it comes from, and only shows stuff that would meet one of the two definitions of Core (except for the Technology Guide, which was put up so that people could more easily run one of the adventure paths which is technology based iirc).

[Tabris623]

So Summoner was vetoed by my GM (specifically because of that archetype) but I alchemist seems more and more hilarious for this and other reasons as I read into it so I am definitely do that. Thank you so much all of you.

[Psyren]

Alchemist has several ways you can do this, have you thought about which one? Standard Alchemist with select discoveries and extracts? Beastmorph (+Vivisectionist)? Metamorph? Master Chymist?