I am very firm against the use of Ultimate X and Black Zero. All you have to do is spam the Ultimate Strike (for Zero, he's just so much more godly) and you win. There is absolutely no skill involved at all. There's not stage planning, there's not jump planning, there's not Special Weapon use planning, there's nothing but you and the Z button (or whatever Giga Attack is set to). The only thing you'll have to worry about is Giga Attacking into spikes, I mean seriously.
Dark Chips, I'm not too familiar with. They are rather game breaking as I think Dark Sword does like 500 damage and it acts as a Life Sword, just not a PA. I say I'm against them, but I don't know much about the Dark Chip using Battle Network games.
Glitches, though, is fair game.
Also, it's not the fact that it makes it too easy, it takes away the skill involved in playing. You're pretty much proving nothing if you are just spamming Z. I mean, you're invulnerable, you have infinite, you move faster (I think it's the same sped as having a Speedster equipped) and it does massive damage (stfu Gerbil >_>). It's more than game breaking, heh. :x