(Pathfinder) Playing as pure monsters (no classes) and evolution

[Yamegawa]

Recently I ran a One-Shot where the PCs were monsters they chose from the bestiary (CR 1 or lower) with no class levels, instead they had a custom ability I though up.
Basically, any character could eat a part of a recently dead creature, and gain one of the following:
a) the creature's bonus to an ability score added to his own (after removing size modifications)

b) one of the creature's feats (treating ability to use weapons and armor as the corrisponding feats)

c) one of the creature's class skills (like sneak attack, channel energy, the ability to cast one of the spells he had prepared as a spell like ability 1-3 times a day, ecc...)

d) an anatomical part of the creature (natural weapons, armor, tail, wings, bite attack, breath weapon, senses, etc...)

e) a hit die


Yes, rather complicated, and extremely overpowered, but we all had a great time. They went from having to ambush goblins to steamrolling an adult dragon, and loved being able to grab whatever random thing they wanted from their enemies corpse and add it to their repertoire.

The main issue is that I have been asked to run a small campaign (no more than 8 sessions) based off this concept, and I am quite frankly out of my depth. I am by no means an expert on Pathfinder (been playing about a year and enjoy reading rules, but still lack a lot of experience) and them asking to play with this idea some more in a longer running setting was unexpected. Any help with making this work, or at least making something that's similar in base concept, is greatly appreciated.

My idea was to limit the evolution ability so that you can permanently store a number of things you steal equal to the number of hit dice, as well as two temporary slots that expire 24 hours after the power is gained. Permanent slots can be replaced by a temporary power, but the replaced power is lost. As for the options, remove the bonus hit dice option.
Help with this would be awesome.

The other thing that has me in trouble is the fact that most want to use custom monsters (either weaker versions of existing material or their own brainchild) and since in their place I would too, I would like to try and make it possible if it can be done. I have found a nice JavaScript program called MonsterGenerator that is a tool for creating monsters of a specific CR, and I thought I could just use that to help them create their monsters and still have some semblance of balance by the end of it. If anyone has any ideas how to make monster PCs, I would love to hear them.

Sorry for the wall of text, and I thank you for your help.

[Anachronity]

This isn't a concept that can really be balanced, per se. The best you might manage is to get it to spiral out of control a liiittle bit more slowly than last time. But it seems like you know that.

I would recommend just telling them to keep it somewhat reasonable, except that Pathfinder is a complex system and it's hard to readily know what is and isn't strong without a lot of hands-on experience.

There's a Pathfinder race creator described in the 'Advanced Races Guide' and available on the OGC (which I'm not sure if I'm allowed to link to?), but some of the point costs are way out of wack, and there's zero guarantee that one monster is equivalent to another with the same point total. Breath Weapon is a good example of something that's hilariously overcosted, while bonus feats and getting higher attributes are undercosted.

[Miko_Kira]

Change the rules? You could create a monster-class level. Make a limit on the number of mutations per level. Mutations can be swapped out as they 'evolve' trading out a current mutation for a new one. Undead, constructs, and the Tarrasque (for obvious reasons) are off limits, unless otherwise mentioned. Example; Jason Voorhees became a cyborg in Jason X.

You could also set a limit on what abilities can be obtained, or have them scaled to match the character level, so it provides a more consistent challenge.

I can guarantee, I would 100% eat mimics for their abilities, hide out in the open and become a general menace to anyone that happens across me. "They attack the gazebo for a reason. I am that reason." - Me probably.

[Yamegawa]

I saw the rules for creating custom races, but the prices are really out of whack. Another interesting find were the Eidolon evolutions for the Summoner class, they seem pretty cool, but really limiting to a melee only style.

Since it only needs to last about 8 sessions, and wealth will be much less (and naturally harder to spend) it just needs to last long enough that a crusade of high level NPCs is a fun challenge in the last session.

That's a good idea about making the powers scale with level, I can use the original formula for damage and DC that monsters use, that way it encourages them to not focus only on one ability and be a bit more well rounded.

I am indeed going to try and limit the fallout of the powers, and I'll try my best to avoid giving them insane powers (like the permanent greater invisibility of a Lurker in the Light, or Wish as a spell like ability from a Djinni) and I'll speak to the players about min-maxing (they don't normally do it, so it should be fine).

About the Mimic, last session they actually found and ate a Deathtrap Ooze, so a few started turning into giant wall scythes and rolling rocks in later fights, very hillarious.

Thanks for the help