Revengeance The Octagon are a joke.
Except when they destroy your world.
The Octagon eventually misuse their powers in an alternate future of Earth-0 and result in the cataclysmic death of billions. Climate change, famine, plague, fascist police-states, death camps, starvation, dogs and cats living together, the works. The Octagon, just as before, evacuated the world to carry on their nasty business on another world. This time, however, the remains of Pendulum were ready for them.
They selected one superhero to go back in time using a cosmic-string theory device that allowed them to actually find the one universe in an infinite sea of them where the Octagon's activities could be prevented. It required virtually the entire energy output of their dying world but the opportunity was too good to miss. Revengeance believes that the few survivors of his planet died after this, which is probably accurate. It, however, only adds fuel to his quest.
Or her quest. It's not exactly clear.
Revengeance is a superhero of the 21st century but no one is sure which superhero he or she is. Revengeance's outfit with its iron mask, heavy cloak, and voice synthesizer is doing their very best to hide their identity. There's a practical reason for this. Due to the fact time-travel is actually altering the future this time, if his or her past identity is killed, Revengeance will disappear from the face of the Earth. They can't allow that until their mission against the Octagon is done.
This opens the opportunity for GMs to decide who Revengeance might be. It might even be a PC if you are so inclined.
Given the Octagon are a goofy but genuinely malevolent group of people, Revengeance's quest isn't necessarilly a bad thing. It's just the decade or so of living hell they endured before time travel has kinda-sorta driven them insane. Revengeance is quite rationale, really, it's just it's the sort of rationality that has difficulty explaining why they leap out into the middle of a shopping mall to stab a seventeen year old in the neck. Explaining said person was eventually joining to open a death camp is unlikely to fly. Because while the Octagon are Revengeance's primary target, they're far from the killer's only one.
Collaborators, war criminals, future supervillains, and so on form a vertible Santa's clause list of naughty or nice. Revengeance is believed to be nothing more than a superpowered serial killer at present, especially given some of the particularly nasty ways they've disposed of their victims. The relatively minor member of the Octagon known as the
Tick Tock Terror was clubbed over the head before being fed to carnivorous rats.
Revengeance is an amazingly skilled assassin, having been purified as a warrior in the dystopian future the Octagon create. Likewise, he's armed with all manner of amazing gadgets taken from other heroes. This incredible bag of tricks has surprised virtually every hero or villain who has encountered them, often seemingly appearing at random to thwart their capture. Quite a few people would love to have access to this bag of toys, especially those who suspect Revengeance comes from the future.