It's so cold down here, and creepy, when lit only by the purple glow of the mysterious crystals. And there are... Black pools among those crystals now, with shadows that are surely of the sort Anthem was just talking about.

"Okay, you stay away from that," he instructs, not wanting the shadows to start talking to her if she gets too close. Instead, he swims closer, curiously peering at the darkness. It's like a pool of dark tentacles that writhe and move. Extremely unnerving. Looking around him, he also doesn't see any bodies. Until--

From the blackness, an arm shoots up, grabbing Finnick's wrist with an impossible strength. The arm is laden with crystals, otherwise looking necrotic. He yelps in panic, as well as one can yelp underwater, and jerks backward. The strange hand has a firm hold, so all his movement does is slowly lift a body from the blackness, which is similarly crystallized and undead. But... It does, vaguely, have the form of a little girl. A wisp of long red hair unfurls in the water.

This was Alice. Benjamin's twin sister. Her eyes glow with a sinister violet energy.