7. Superman Red/Blue
Now, contrary to consensus, I'm actually partial to a bit of nineties Superman. The mullet is a great look (fight me), Reign of the Supermen is pretty fun, despite Death of Superman not being all that, and the character also gets his due in Grant Morrison and Howard Porter's brilliant JLA series that kicked off in 1997.
However, for all that I can extol the virtues of nineties-era Supes, there are definitely some, err... creative liberties taken with the character. Arguably the most infamous was Superman Red/Blue, a storyline that reimagined one of Supes' weird Silver Age arcs where the character was split into two halves - a red half,and a blue half, who are both super intelligent - only this time they had snazzy new electric powers.
The reasons for the split differed massively from the sixties incarnation, with the reason this time being that Supes had lost the solar energy needed to fuel his powers. This led to him fashioning a new containment suit that could better handle the nascent different abilities that emerged to compensate for the lack of his old ones.
Now to be fair, the actual electric blue Superman suit is pretty cool, and the idea of Supes having to relearn what he's capable of with new powers at his disposal isn't that bad either. The issue mainly is that the change felt contrived and, in retrospect, borne out of that quintessential "X-treme!!" vibe most nineties super books were going for.
Things only got weirder when Red came onto the scene, with Dan Jurgens contrasting the more contemplative "Blue" Supes with the more brash and aggressive "Red", and it wasn't long until DC reverted the character back to his old self, sparing the details along the way.