These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
One bug on Sabretooth may allow you to throw your opponent without actually making contact with them - though often without any actual damage. Maybe he developed telekinesis as a secondary mutation.
Beast can do the same.
There were tons of 'em. One such bug transported both players permanently into the dimension Nightcrawler travels to in his Lvl 4 Super. This renders the opponent incapable of attacking until either the end of the round or the super attack is done again. A more benign but infinitely more awesome version has both players continue to fight in the psychedelic realm for the remainder of the match.
The levels have several 'glitch points' where the player can breach the Invisible Walls - most characters can charge, jump, teleport or even walk into them.
Nostalgia Filter: The game is buggy as all get out, let's just admit that. But damn if it isn't awesome.