Ururuun

Ururuun (ウルルーン) is the miniboss in Grenade Man's stage. It's a giant eye that attacks by tackling Mega Man or dumping junk above him. It surrounds itself with layers of junk which can be destroyed. It surfaces from the junk pile that is its arena. Defeating it gives you the Rush Cycle. Astro Crush seems to be it's weakness.

Trivia

 * Its name is derived from the Japanese onomatopeia "ururun", which describes drooping, weeping eyes.