DeviantART: http://unownace.deviantart.com/art/His-Own-Worst-Enemy-635093882

...Dramatic metaphors, anyone...? XD

In case it isn't clear, the message I'm trying to get across here is that more than ANY villain, adversary or struggle, Ace's BIGGEST weakness will always be "himself". Not so much that Mirror Ace is his biggest threat, but that the risk of BECOMING like him is. In almost EVERY major struggle Ace has had to face, be it Darth Venomous, the Cyberoids, the Coalition and even cancer, it's always his own mind and body that he has to compete against the most in order to win without becoming one of the very monsters he dedicated his life to fighting. This is why he often considers himself a "Grey Jedi".