Crash Man can also be considered this. He is pretty much the character who can dish out the most damage in a large area with a single shot. The only drawback is that he can't fire straightforward when jumping, and he can't fire rapidly. To put it simply, his weapon can:
Is the only weapon that can break the crash blocks
Can be used to outsmart a Mettaur
If you know how to use him, Flash Man can be an extreme Game-Breaker. For instance, Shadow Man can be very hard and annoying to dodge, but if he allows Flash Man to use the Time Stopper, he can basically damage Shadow Man enough to where a lot of his health will be taken away.
Quick Man. He's extremely fast, can jump high, and can attack very rapidly, making many of the platforming sections rather trivial.
That One Boss: Bubbleman and Flashman, again. Or any boss on anything harder than Easy Mode.
Yellow Devil MK-II.
Zero-Effort Boss: The Guts Tank. Hide up against the blast shield and just keep summoning boulders. They'll break hitting the shield and splinter out, and some will hit the Guts Tank. Meanwhile, the shield will protect you from all harm.