I first called your attention to the bootleg Street Fighter II: Rainbow Edition variation of Capcom's classic fighting game back in 2011, but despite being two decades old at this point, people are still writing new material about this bizarre hacked and copyright-infringing creation that allows players to throw fireballs in mid-air and toss Guile's sonic booms without delay.  The latest person to take it on is USgamer's Joel Snape who has looked back at the game and approached the topic not so much from a technical perspective, but from the point of view of how the game impacted the fighting game community and Capcom itself.  Here's a sample:

"I played Rainbow Edition in the arcades a fair amount," says David Sirlin, lead designer on Super Street Fighter 2 Puzzle Fighter Remix and author of Playing To Win. "It's crazy and not serious, but pretty fun. You had walls of fireballs with Sagat, Dhalsim with insanely fast walk speed, rather than the slowest in the game, Blanka throwing fireballs...fun." 

Then there are genuinely bizarre changes: land Blanka's neck-bite, for instance and the Brazilian monster morphs into Ryu doing a slow-motion Dragon Punch. Players can change into other characters, mid-match, narrowly beating Mortal Kombat 2's playable Shang Tsung to the punch.

For every wildly successful game there will always be gray market imitators.  In the 1990s it was Rainbow Edition and others like it.  Today it's the dozens of clones of mobile hits like Flappy Bird clogging up app stores.  Some things never really change, do they?  Here's another look at the insanity of Rainbow Edition in action as M. Bison and Chun-Li change into Balrog and a fireball-throwing Vega among other matches.