Story related and cannot be missed.
This unlocks after defeating Doctor Doom at the end of the sixth episode, “Offspring of Villainy”. To defeat him, use a couple of regular attacks and then get out of the way of his lightning area attack. Run back in for a couple quick punches and then get out of the way again. Repeat until he rises in the air. Just run around the room in a circle while he tries to shoot at you. At some point he will split into 4 clones. Use Quicksilver and run to the nearest one and press “B”. Now press the corresponding buttons that pop up onscreen to make a circular running attack through the rest of the clones. Some Doombots will drop in so use a heroic attack and then repeat the whole thing until Doom is down. If you do get knocked out, just run over and revive the fallen character with .