[@Keksalot] Karna specifically is not allowed, though, if you are intent on him we may be able to work something out (something being a weakened form of him) In general I am shy of Heroes who combine things like invincibility with massive destructive capacity as well as peerless skill. Achilles is similarly off the menu for the same reasons. 

Other than these few, everyone besides completely fictional modern characters and gods are on the menu.