What if each character had a special move that he or she could charge up for more damage? Have like three normal special moves but a stronger one the opponent couldn't block:

SUB-ZERO *Polar Blast*
Forms a massive ice shield that spreads out after it is released and is unstoppable.

SCORPION *Demon's Breath*
Charges up a large breath of fire and releases it and spreads it around him.

RAIDEN *Heavenly Strike*
Forms a thunder cloud above the opponent and lets loose his most powerful lightning bolt from above.

BARAKA *Rage*
Gathers up all of his rage and he dashes towards the opponent roaring and swing his blades.