Shupponpon

Shupponpon (シュッポンポン) is the train enemy of Mega Man 8 and Mega Man and Bass. In Mega Man 8, they emerge from certain tunnel-like doors in Clown Man's stage. In Mega Man and Bass, they emerge from hidden tunnels in Magic Man's stage. In either case, they ride on tracks and damage Mega Man if they hit him with the front. But Mega Man can ride on them safely if he stands on the platforms on their heads. They are indestructible by normal weapons, only being destroyed if they collide with each other, or hit with Flame Sword, but if they are hit with a weapon, they will get angry, as indicated by their smoke turning dark grey and their eyes frowning, and they will speed up.

Trivia
It's name is based on the sound made by a steam engine, "shuposhupo" (シュポシュポ).