Mega Man 4 NES

Mega Man 4 is Capcom’s 1991 sequel, the first in the series developed largely without series co-creator Akira Kitamura’s direct involvement as director, and the debut of the Mega Buster’s charge-shot mechanic — holding the fire button powers up a stronger blast, a move that became a series staple from here forward.

It also introduces Dr. Cossack as a new antagonist alongside the returning Dr. Wily, initially framed as the mastermind behind the game’s eight new Robot Masters before the story’s actual twist plays out. Releasing as the NES was already losing ground to newer 16-bit hardware, it’s often cited as the point where the series’ Robot Master gimmicks and mechanics started feeling more iterative than the earlier entries’ bigger structural swings.