It is actually possible to "kill" Doctor Wily in the penultimate boss battle with him. After destroying Wily Machine No. 4, switch to Toad Man's "Rain Flush" weapon and fire it so that the screen-clearing rain comes down before Wily leaves the screen in his escape pod. The attack will destroy him with a sound effect and explosion graphic the same as if you were destroying a common stage enemy. Mega Man will now be stuck on this screen forever, as the game does not move on to the next level if you do this.