Buck

Brace is a Transformer from the IDW portion of the Generation 1 continuity family.

Buck has a beast mode. We're going to go out on a limb here and say he probably turned into some kind of hoofed creature.

Fiction

IDW Generation 1 continuity

Buck was one of the many beast mode Transformers who had been kidnapped and subsequently "domesticated" by the Decepticon Demus. Intended to be sold off as a "Roboid" torture doll, Buck and his fellow prisoners were freed thanks to Fortress Maximus and the Scavengers. Animals Maximus brought them back to Luna 1, where the surgeon Cerebros began repairing their internal injuries, restoring their higher functions and robot modes. Buck was still awaiting this treatment when Sentinel Prime attacked. Ten to Midnight