Awesome: Sonic The Hedgehog Mega Man Worlds Collide
Let's start with a meta example. Once Archie had finally gotten the rights to make a Mega Man comic. Ian Flynn wasted no time in planning out the crossover. This was well in the works before Mega Man even started his first issue!
Wily and Eggman. Not only is their bromance entertaining enough on its own, the way they manage to play Sonic and Mega Man against one another, in addition to rewriting both of their realities, is nothing short of a villainous triumph.
Sonic gets one in Sonic the Hedgehog #248, where he turns the tide of the battle against Mega Man (which had been a stalemate up to that point) by using his wits and the unique geography of Green Hill Zone.
Likewise, Doctor Light gets one when he figures out how to recreate Eggman and Wily's interdimensional portals simply by analyzing some data given to him by Blues.
Sonic and Megaman finally becoming friends in Megaman #25.
Copy Robot and the Genesis Unit versus Sonic, Tails, Mega Man, Proto Man, and Rush in Sonic Universe #52.
Tails modifies Mega Man's buster to fire out Spin-Dash Blasts. In the middle of a fight against the roboticized Chaotix, no less. Then MM uses it to cure the Chaotix Roboticized Masters along with Sonic's help.
Part 9. Nearly the whole thing is a battle royal between Mega Man and Sonic's team versus what was described as nearly 100 Robot Masters turns out to be every Robot Master from 2-10, plus King's Robot Masters and the Genesis Unit the only ones who aren't there are the original eight. It is glorious!
The splash page showing Mega Man, Sonic, & friends facing off against them all counts as a meta example. Of the 82 Robot Masters (counting the roboticized Rouge Woman), 81 are visible descending upon the heroes (Flash Man is missing until a later page). Ian Flynn described the page as "the moment [he'd] get death threats from the art team."
Part 10. In addition to the continued awesomeness of the fight, Dr. Light gets a moment when he crashes in the middle of it. After making sure Mega Man and Sonic are in the Wily Egg, he constructs a Buster and joins in.
Part 12, full stop! The original8 Robot Masters arriving to help our heroes with the 2-10 Robot Masters.
Sonic and Megaman going Super! Especially their epic Combination Attack that dispatches the Egg-Wily Machine X in one shot.
Duo makes quite an entry in the comic, dashing through multiple floors of the Wily Egg and uppercutting the freaking eye out of the Chaos Devil!