Chill Bullies resemble their non-icy counterpart, except for having two horns, it only sports just one spike atop its body. As mentioned before, the body is made of ice, while a Bully's body is black and made of steel.
A Chill Bully appears there as the Fortress boss of World 4. It is basically a weaker version of Chief Chilly, it's leader, who appears in the same game as well. Mario has to push it in the cold water with his Spin Jumps, before the Chill Bully does the same thing to Mario.