Well that's a really nice edit, and I hope you can edit the gethits, crouch and jump sprites.
As for some attack ideas:
*Chargeable cero: the longer you hold it, the stronger it gets.
*Multiple punches: something like johnny's gin attack
Spoiler, click to toggle visibilty. Grimmjow used this on ichigo in their first fight.
*Running stab: Press attack command while running, grimmjow uses sonido and stabs the opponent with his hand/sword. He used this on rukia the first time he invaded karakura. (Or you could use the idea for an hyper, just like the stormex-ogihci's one)
* Grab the opponent and blow it away with a cero. He used this against ulquiorra, and whe he saved orihime from the female arrancar.
As for ulquiorra, They were never closer as friends or something, I don't think that would fit grimmjow at all(same goes for any other helper)
Good luck with the project!!!