Story based, unmissable. If you do not wish to spoil the game, just play thru the game and you will get this before you finish the story campaign. If you are a little curious, open
Mini Spoiler but don't open
Big Spoiler.
Mini Spoiler
Big Spoiler
*** Spoiler - click to reveal ***This will unlock toward the end of the story campaign, in the second to last main mission, which is called The Many Assses of Dr. Mephesto. It is the very last step in this main mission, which is a fight with Mutant Cousin Kyle.
The strategy here is to shift time from Night to Day (and then again, and then again), which buffs your damage for a limited time to something like 2x (or more?). You will not be able to do this right away, just fight normally until it becomes available. Stay away from the boss and revive/heal your downed allies, save your supers for when you're in double damage mode. Took me 2 tries (beat him on second try). I think I hit him with a super in 2x damage mode at least twice.