Snakey

Snakey is the giant snake "mini-boss" of Mega Man 3. There are two, and as one can suspect, they only appear in Snake Man's stage. When facing them, there is a moving "floor" (it's tail) to make the battle difficult, as it shoots multiple shots. There are small and big snakeys.

Fun Facts
Coincidentally, there is an Adventures of Lolo series enemy also called "Snakey", but this tends to be the easiest "enemy" of said games. All they do is stare in your direction and just sit there. They often serve as "blockades" to more dangerous enemies, such as Gol or Medusa.