Paint-like Goop
It was the aftermath of Leviathan's attempted attack on Brockton Bay. Emphasis on "attempted." Thanks to the Celestial Forge, Leviathan was defeated soundly, with no casualties on the side of the defenders. But, the weapon used happened to have a side-effect...
"What's this icky, paint-like goop?" Vista asked, the Wards huddling around a large puddle of glowing green goop.
"It's moving..." Tattletale shivered, clearly unnerved by the glop of substance. The rest of the Undersiders eyed the puddle with varying levels of interest.
"N-Now, now, children," Apeiron called, rushing over, looking a little panicked. He paused upon noticing the Wards were there as well. "...and also the Wards! Don't touch that stuff!"
"Can I eat it?" Vista asked, directing a plastic smile laced with exhaustion and begrudging gratitude towards Apeiron.
"Uh, no, that would... involve touching it."
Vista's smile turned smug. She placed her hands on her hips and leaned forwards slightly. "What if I already did?"
Apeiron pulled out a massive PDA and started poking at various buttons, producing many beeping sounds. "Well then, you'll probably explode," he reported.
Vista nodded as if this was expected. "Oh, okay..." she replied, turning her attention back towards the puddle of bubbling green gunk.
Vista suddenly wrenched her eyes back up to Apeiron's helmet. "Wait, WHAT?!" she squawked, before the Bay was enveloped in a nuclear explosion.