There are some situations where a PC's intelligence may drop to animal levels due to ability damage/drain/burn. I would like to know how they act and do they still have access to class features and feats that they have acquired? I would assume at this point they wouldn't be able to speak either since humanoid intelligence ends at 3.
[RPG] How to handle PCs with 1 or 2 intelligence
dnd-3.5epathfinder-1eroleplaying
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You're trying to use a D&D precedent in Pathfinder, but the Diplomacy rules were specifically changed!
The line "You cannot use Diplomacy against a creature that does not understand you or has an Intelligence of 3 or less" was explicitly added to the skill description in Pathfinder; it was not present in prior incarnations of the rules. Given this, it hardly matters whether it worked in 3.5 or not.
what is this witch ability good for if it doesn't allow for using diplomacy?
Um, talking to animals, same as the spell it emulates? You can still get information from them. I believe you could also cast [language dependent] spells on them, if you want a more specific game benefit.
Probably yes, a sorcerer with an Intelligence score of 2 yet possessing sufficient Charisma can still cast spells with verbal components
The GM can rule that a low-Intelligence sorcerer can't cast spells, but the game doesn't outright say such a sorcerer can't cast his spells. Therefore, ultimately, the GM must decide. That's because according to Components
A verbal component is a spoken incantation. To provide a verbal component, you must be able to speak in a strong voice.
While Pathfinder has several sets of rules for things called incantations (e.g. here, here), the term incantation as mentioned in Components is undefined, so the GM can then consult his favorite dictionary and use that definition of incantation to tell the sorcerer player No spellcasting for you.
Further, the GM may rule that the sorcerer's low Intelligence score makes him incapable of verbalizing at all, dropping the poor sorcerer back to the prelinguistic stage of language development.
But, assuming that the GM doesn't want to player to head off to the other room and play Smash Bros. until the sorcerer's Intelligence is at least 3 and that the player appreciates the challenge of role-playing, essentially, a dog with a built-in shotgun, the DM should permit the low-Intelligence sorcerer to cast spells.
Note that I would be very wary around a dog with a built-in shotgun, especially if that shotgun were reloaded automatically each time the dog wakes up from a long nap. I'd go to great lengths to keep that dog fed, happy, safe, and appropriately amused.
Because it's been referenced in several Comments, in Pathfinder's antecedent Dungeons and Dragons 3.5, under Monsters as Races it says
Creatures who have an Intelligence score of 2 or lower, who have no way to communicate, or who are so different from other PCs that they disrupt the campaign should not be used.
Then, later under Ability Scores for Monster PCs, it says
The separate table for [modifying a PC's] Intelligence [score when the PC is a monster] ensures that no PC ends up with an Intelligence score lower than 3. This is important, because creatures with an Intelligence score lower than 3 are not playable characters.
Neither artifact, so far as I can tell, appears in Pathfinder.
Best Answer
The closest I can find to relevant RAW is in the rules for monster races:
But this doesn't necessarily mean that a PC with temporary int damage should be made an NPC.
I'd definitely allow any feats they haven't lost the prerequisites for. (Animals have feats, after all.) Same with class features; only those explicitly requiring intelligence (such as wizard spellcasting) should be lost.
Can they use skills? Can they speak, and understand speech? Well, in 3.5 you don't retroactively lose or gain skill points due to a change in intelligence. So, I guess strictly speaking yes! (And again, animals get skill ranks.) The PC will probably have more ranks than an animal, but this isn't as strange as it seems -- intelligence is described as "how well your character learns and reasons." Losing intelligence doesn't necessarily make you forget what you've already learned.
I'd probably use the pathfinder rules (which were certainly a common houserule in 3.5), and say that permanent changes do have an effect on skills and languages, Flowers for Algernon style.
So, other than simple penalties on Int based checks, and the loss of any abilities with an Int prereq, there aren't many mechanical effects here. It should absolutely have a large effect on how the PC acts (really large! they're dumber than a toddler!) but that's more of a roleplaying thing. I suspect most players would play it for comedy, but tragedy is always an option.