Shaco: Giving him some depth, some nasty personality, and some sheer badassery
Shaco right now has a pretty bland Joker-wannabe persona going for him, one that I think could be done so much better. His story is also kinda unimaginative and doesn't allow anyone to really get a feel for him as a character.
With that in mind, I have someone he could take notes from.
Yuki Terumi of Blazblue
http://img1.wikia.nocookie.net/__cb20130517150226/blazblue/images/b/b8/Y%C5%ABki_Terumi_%28Chronophantasma%2C_Character_Select_Artwork%29.png
This guy is a total bastard. Kicks you while you're down (actually, he STOMPS ON YOU while you're down), constantly hurls insults at you while fighting you ("Sucks to be you!" and "You're too weak!" for starters), and he's also a downright badass schemer (hard to explain his schemes in short form).
I imagine Shaco could do the same. He seems like the type who'd take a piss on your carcass if given enough time, just to piss you off (ba-zing). Plus a persona like this one could help make him a little more separate from Jinx, who does the "bat-shit insane psycho" role better.
Anyone wanna add?