This is Nate in their soul form, an incorporeal figure with the ability of creating a vessel in the shape of their real body, "reviving" them.
It won't do any harm and it can't be harmed in any form, unless the creature it's dealing with can manipulate, destroy or consume souls, which could mean Nate's permanent demise.
Alt of IllusionistNate (Click for full character's info)
--All the times their vessel broke (AKA "died" as their body), revealing this form--
#1 (December 25th 2022) - Turned into cookies by Foxy_Mindy.
#2 (December 26th 2022) - Swallowed alive by The_old_one in their female form, then digested along with the cookie they tried to bribe their way out of her grasp. (And every other cookie inside their robe)
#3 (December 28th 2022) - After having their ass violated by tentacles summoned and controlled by the following pred, they were swallowed by The_old_one (in their female form once more), but through her pussy, sent into her 'tunnel of love' to have their body melted with two more "unfortunate" preys inside her womb.
#4 (January 6th 2023) - Presumably shrunk, then brought into a cookie costume by Foxy_Mindy and offering them to Niiko who proceeded to swallow them whole. (Blame the player for leaving them to become the catboy's nutrients so that had to happen.)
#5 (January 8th 2023) - After they brought Niiko into their own cave for a nice visit, around the spooky boneyard, the two had the idea of trying some cookies with an experimental potion that made the catboy grow larger, wild and very hungry, having Nate as his own "mouse snack". For some reason, the potion didn't do much effect on Nate themself, but at least they had a nice trip.
#6 (February 3rd 2023) - After being inflated by Foxy_Mindy, brought to the skies, falling and getting stuck on a tree, they were freed from the branch, only to fall right into the fox lady's maw, being swallowed whole and digested right away.
#7 (February 10th 2023) - Turned into iced-cream cookies (?) by Foxy_Mindy then eaten by the clueless Niiko.
#8 (February 16th 2023) - After grown by one of Foxy_Mindy's spells, Nate was swallowed even while about 5 times bigger than the pred.