Whopper

Whapper (Nintendo Power calls him "Spring King", for some reason) is a mini-boss in Mega Man 4, and like Hippoplatter, there are two of them in Ring Man's stage. It is vulnerable when its eyes are open, but that is also when it launches its rings in six directions. A few charged shots will destroy it easily. Two Drill Bombs will also work. The Flash Stopper can be used to freeze time and take the Whapper down easily, but the rings that were launched will still damage the player if they are touched.