The Mimic (Patreon)

The story is some horny wizard or something decided to modify a mimic to make it a little bit more "helpful". He ends up making it way too aggressive for his liking and ditches it somewhere secluded.

Cut to a guy who turns into a werewolf every full moon, and to avoid hurting anyone he goes to said secluded place every time. But one of these days, he wanders a bit further than usual and stumbles upon a chest with a broken lock...