https://files.facepunch.com/forum/upload/224422/4b22f28a-aef0-41db-be31-b9229ba67bf4/2015-10-31-beartato-trickortrick.png
Beartato is not wearing a costume. He looks this way because of a problem.
Uh...context? Did he like, eat bad Taco Bell smothered in Diablo Sauce or something?
Linked because implied spoilers for Endgame:
https://i.kym-cdn.com/photos/images/original/001/489/927/826.png