Jackhammer is one of the few brave enough or stupid enough to willingly remain on Cybertron during the threat of the grand Black Hole caused by the destruction of Unicron. He appears to be the brains between him and Crush Groove, but this seems like a fairly low bar. Jackhammer's alternate mode in unknown; he has hints of perhaps a walking vehicle similar to a Scrapmetal, though circular objects on the backs of his legs might be wheels.