Victor Fries, driven mad by the loss of his wife, wears a cryogenic suit in order to survive, and bases his crimes around a "cold" or "ice" theme, complete with a "cold gun" that freezes its targets solid.
Mr. Freeze teamed up with Toyman to use Kryptonite Man for nefarious purposes. When Supergirl and Batgirl came to bust up the operation, Mr. Freeze attempted to shoot Supergirl with his ice gun. However, Stephanie jumped in front of her and disabled the weapon by throwing batarangs at it.
Kara smiled and said, "You do know I could have taken that, right?" and Stephanie shrugged and said she had to pull her weight in the team up, because Kara "took out Toyboy and I owed that little jerk".
However, the fight was not over, as Toyman attacked the girls with a huge composite Superman/Batman robot! Stephanie managed to call in a "code black" (highest level threat) to Oracle before the link was severed. Oracle called in Superman and Batman.
Steph was rescued and she and Damian went after the villianous duo, Steph taking Toyman and Damian taking Mr. Freeze. However, Damian apparently didn't do his job well, because Mr. Freeze froze both him and Batgirl, saying, "What is it the kids used to say? Oh, yes. "Chill ou-" but Superman interrupted him with an "Ahem. Freeze." and Supergirl melted the ice around Steph.
More on Victor Fries here.