Writing about Super Smash Bros for an article covering fan service is a bit of a cop-out. The series is literally nothing but fan service. Since Melee, every Smash game has dived deeper and deeper into the history of Nintendo, pulling out references from nearly every product Nintendo has put out. There are callbacks to characters from games we haven't seen in years and products Nintendo hasn't made in decades, with Smash for Wii U and 3DS featuring the most extensive historical record the series has seen yet.
Really, going into this topic I was planning to write about Duck Hunt Dog calling in the NES Zapper Posse to blast his opponents away. As much as I love that, it ain't got nothing on Mega Man. Mega Man's Final Smash is a celebration of a series people assume Capcom didn't care about for the longest time. Hell, Mega Man's appearance in Smash is the most love and care given to the character in nearly a decade. With his unique move set, Mega Man easily outshone the other 3rd-Party guest characters. With his Final Smash, he outdid the rest of the cast.
I don't remember where I was when I first saw his final smash, but I do remember my jaw dropping and nearly crashing my browser reloading the YouTube clip. Even though I prefer other characters, I made myself get good with him just so I could see Mega Man, X, EXE, Volnutt, and Star Force come together in one spectacular finish. It's so frickin' good that if Mega Man returns in Smash Switch, I wouldn't mind if his Final Smash was left untouched.