Basictek

Villain has some tech from Mr Freeze…

What episode?

Season 3, episode 4 "Antifreeze". More will probadly happen in future episodes.

Also supposed to be cryofrozen in episode 3x3, but before you waste your time: instead of inserting nitrogen into the cryo tube to preserve her, they just induce cold air to kill her. She gets saved in the end. I'd start at 1:40 for the scene where she's in the tube. Also, some kids steal some nitrogen and open it in the back of a transit bus, encasing the entire bus and everyone inside in ice. On a side note: some fine looking ladies in this show...

https://youtu.be/fm5IltYY4os

I mean it's a CW show, if their protagonists don't look like they could be the starts of a romance novel aimed at teens then the casting director is fired.