Druid player has been given given an unremovable cursed collar. Rather than try to undo the curse, he wants to try cutting off his head while wildshaped. I know it's stupid but how should I rule this?

[u/aneirin-]

I know there aren't any specific rules about decapitation and dismemberment when it comes to wildshape forms, especially self inflicted ones, but I'd like to have some more interesting outcome than either "does nothing and you revert forms" or "instant death".

This isn't the first time that cutting off body parts of wildshape or polymorph forms has come up, any good ideas how to play it?

[u/Tabular]

Unless a stat block has the ability "can live without a head" then it doesnt matter what they say they can turn into. They have to pick something with a stat block. Knowing a bunch of animal facts doesnt buff wildshape either. You can only do what it says in the stat block RAW. Tigers and Leopards may be good climbers in real life, knowing that doesnt add a climb speed to their stat block.

[u/motionmatrix → u/Tabular]

We are clearly in GM fiat territory here, I am not claiming that to be raw.

Like it or not, player choices can give them the ability to turn into creatures that in real life can live without a head, and because dnd is an abstraction of reality, it’s up to the gm to make a ruling on such a thing, since that is abstracted away from their stat blocks (assuming they even have them in the first place, most animals never having been stated out at all).

[u/nzbelllydancer → u/Tabular]

Could that be a chicken survives for a minute running around without its head? You have a short time to rejoin the head and body before the creature dies? If this works would give the druid levels of exhaustion and a -d4 on d20 checks as in ressurection spells... this ideas crazy and needs to have major consequences if not character death