Cold knocks a block of ice free from his makeshift igloo, and sees the battle raging around him. "Oh, Christ..." Kicking another block out, he slides from underneath the structure and sees the vampire attacking Robin.

It's simple math, really. Try and run, and get potentially eviscerated by one of these nasty critters. Side with the guy you know won't kill you, and stand a better chance of living to fight another day. 1+1=2. Or something.

"Hey, asshole!" He fires off a blast of cold power towards the vampire attacking Robin, hopefully allowing the hero to escape the immediate danger.