And before people ask, i was planning to use the Jim Corrigan Spectre, but then giving it some thought as i read his backstory, i realized that the similar could happen to... Well, the hero i chosen due to his death as he died because of some bullshit injustice (Ha, another pun) dealt to him by Superman and the Regime, hence becoming the Spectre and making sure that they're the first one's he goes after. Plus, good plot twist, yes? Also, there are hints, both obvious and hidden, look for 'em.
If you're unfamiliar with Injustice, the characters are divided into two types: Power characters and gadget characters. (This isn't entirely accurate, as it's pretty much characters that have super strength and characters who don't) They use the objects in the stages differently. If a power character interacts with a car, they can pick it up and slam it into their opponent. Gadget characters can slam opponents into the car, jump off of it, or jump off of it and leave behind an explosive. However, some gadget characters (like the Flash) have no explosives and cannot do that last thing.