Signature moves are back in the game, but using them and whatnot is different.
You know how the HUD for your character is now underneath your character instead of in the left/right-hand corner of the screen? Well, with that, they have had to change how Finishers and Signature moves work. Now, when you get your momentum to say, 80-99 of its maximum, then you can use your Signature move. Hitting this gives you an instant Finisher, however, you can still get your finisher without needing to hit your signature move.
Finishers are also different this year. When your opponent counters your finisher in earlier games, that would be your finisher gone. Not in 2010. Instead, you have your finisher for a set amount of time (I think its 15-30 seconds) and in this time, it can be constantly countered and you can still use it. When time runs out, your Momentum goes back down to 50.
Also, some of the abilities (yes, abilities are back) require momentum to work. For example, a new ability, which lets you roll out of the ring when you're on the floor and near the ropes, requires you to have at least 20 momentum to use, and takes up that amount. (This is only speculation on my part, it probably requires less momentum to use).
Also, I think they trashed Resiliency all together (since it was, y'know, broken), but i'm not 100 sure on that.
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