Rug Bear was first seen in the dining hall of Hogback’s mansion. It was later revealed to be some sort of flat zombie creature during the skirmish with the painting zombies and Nami, Usopp and Chopper. Later, when the rest of the Straw Hats entered the mansion and fought with the painting zombies in the dining hall, it was defeated by Luffy with Gomu Gomu no Bazooka. Luffy, upon defeating it also commented that if they weren’t enemies he would’ve asked it to join his crew.

He later reappeared among the surprise zombies screaming in surprise at Oars being knocked down by Luffy

(Source: One Piece Wiki)