http://www.youtube.com/watch?v=gGL9y63d3ysAn interesting mechanics video on the Crossover Counter Assist-call thing (CROSS COUNTERRRR~!!!). Your assist you call in is totally invincible during the jump in until they perform their assist, then they take on properties of that assist (in terms of invincibility and stuff).
So if you Cross Countarrr with Haggar Lariat in a blockstring, he'll be able to super-cancel into his spam-puncher as if he did his lariat himself.
The most interesting/DISGUSTING use of it is actually cancelling the invincible jump down part of the cross counter into an aerial hyper. The disgusting example they use in the video is Sentinel who's Hard Drive is TOTALLY INVINCIBLE and since he does it so damn low, if it pushes them to the corner, he can combo right after it, potentially catching assists as well.
So if your character is about to get chipped out, 2 stocks and you can potentially catch them with absurd Senti-gayness and an absurd combo.