Cell's life in hell was miserable, nothing to do but sit and listen to Frieza constantly blather on about how much he hated that Saiyan monkey Goku. The same Goku cell had killed during the end of the Cell Games, a feat Frieza kept being sorely reminded of. Enter another villain with the magic to give Cell his body back, but with a price. He must go to another world and conquer it for the Wizard, that wizard being Babidi. And imgaine the latter's dismay when Cell renigs and uses it as a means to escape instead. This is on top of the fact that world Cell visits is Equestria. And of all the ponies to pick a fight with... He targets Rainbow Dash and her friend Twilight Sparkle.
To top it all off, Twilight discovers a part of herself she didn't know about, one that Rainbow Dash, nor even Cell had any information on. years ago, a lower class warrior had visited Equus in the name of Lord Frieza. After seeing what the creatures were like, this warrior took a risk and spared them saying that they didn't pose a threat. Also, he decided to take one of them as a " conquest" before leaving. He roughed her up a little but wasn't over all cruel or mean.
Now several forces were set to collide. And the fate of the pony race was up for grabs. And to make it worse
Cell comes to realize he should never cross an Alicorn with the power to destroy a planet. More so, don't piss off the offspring of a lower class saiyan.