When I saw the word "Desperation", I thought DBZ HD for Super Nintendo. When any character then that game got low on health, they could unleash a last resort/final assault or direct attack.
Vegeta's - Grab the opponent, throw him to the ground, fire a barrage of ki balls (about 10-12) down at the opponent, then launch a huge big bang attack to finish it.
*Vegeta's would be sweet for a desperation grad move. If he had that, no player would go near him once they see his PL going down on the scouter. And in the DBZ series, Vegeta is at his best when he seems at his worst.
Goku's - Teleports infront of the opponent, hits him with a bunch of left/right hooks, goes SSJ3, uppercuts the opponent, jumps back, desends to saiyen, and launchs a Genki Dama.
*Goku's would be good for a flashy combo; a show of power. But, probably wouldn't work.
Freeza's - Charges up within a red barrier, then charges fist 1st at an opponent.
*Freeza's would more of an add-on to his normal swoop attack. But, it would only work if your HP is at 1-5.
The others ones are pretty much punches ending with uppercuts.
:yes: Upside: Awesome attacks. Offers a nice counter-attack for players getting the snot beat outta them. Characters would seem noticably different; more reasons to pick character (a) over (b).
:no: Downside: New stuff = More needed animations, coding, and sprites. It would be a ***** to balance the game out. Vegeta has a cool desperation attack that does uber damage, while Gohan, Krillan, Cell, has... you get my point.
