The "chargable weapon" featured as the biggest change to the series in this game is not original. The idea was first implemented in Megaman 2, with the "Atomic Fire" weapon, which could be charged up to deal increasingly more damage (and drain much more weapon energy).
First appearance of Flip Top, Mega Man's ?suitcase?. Flip Top was later named Eddie (he was always called Eddie in the original Japanese version, and the American version later changed to reflect this.)
All eight Robot Masters in this game would appear in two Game Boy spin-offs. Dust Man, Skull Man, Dive Man and Drill Man would appear in "Mega Man III". Toad Man, Bright Man, Pharaoh Man and Ring Man would appear in "Mega Man IV".