Originally Posted by Mr. Dent
I'm not entirely sure what the rationale for the twins wearing costumes will be.
Escalation, as Gordon put it in BB. We got this colorful bunch of heroes gaining notoriety among the public after the battle in New York, so the villains retaliate with their own gang of misfits that would instead garner infamy, while simultaneously providing a distraction for the real mastermind as he works in the shadows. Quicksilver's costume also doubles as an outfit that would provide resistance to the negative effects of his powers.