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.
Game Breaker: Taffy and Ickybod Clay in the first game, because the former had long reaching attacks & the latter could teleport.
Also in the first game, The Blob. His signature buzzsaw move(where he'd turn into a saw blade & rocket towards his opponent) used to hit the opponent repeatedly if he or she blocked, dealing more damage then it is supposed to! Nowadays, it just stops when the opponent blocks.
Porting Disaster: The Sega Genesis version, which was picked for Virtual Console release.
That One Boss: The final boss of the first game, who constantly lobs projectiles at his opponents. These projectiles also happen to be from the other fighters. Add in a sick grab move & you have one tough opponent to beat.