Outcasts could have Two Bosses called "Chiller" (all ice-powers) and "Zero Chill" (firebased).
Frostfire is just small-time compared to Chiller.
There could be an Outcast-Storyline for levels 45-50 concerning these two.
One mission you fight Chiller alone.
He is quite reluctant to fight at first, and it is evident in the dialogue that he prefers to chill instead, but eventually will Fight the Team, bringing all his frosty minions.
The longer the fight takes, the colder its gets in the room.
For each 30 seconds of fighting (Chiller will try and Iceblock himself at least 3 times in this encounter so it could take a while), the Team suffers a Recharge and Movement penalty.
If you cannot defeat Chiller within a certain amount of time, it will become a slog, with people moving like they are on caltrops, and recharge of the powers being very very slow.
Finishing Chiller before he can Iceblock himself is main objective in this fight.
Another mission you fight Zero Chill alone.
He is very aggressive, attacks from the get-go and on sight with Fireballs, Firewalls and whatnot.
From the Speakers in the Boss-room you can hear a faint:
"I am the god of hell fire, and I bring you! Fire, I'll take you to burn. Fire, I'll take you to learn. I'll see you burn!"
The Team takes damage constantly each tick, and the Damage of the Burning room gets higher the longer the fight takes, so it is important to finish Zero Chill fast.
Finale
Then in the Grand Finale of the Story-Arc you face them both together, and the longer the fight takes in that Room, it becomes Hot and Steamy.
More and more Smoke/Steam will cover the room making it difficult to see for the Team, so the final fight will have a Time Limit of sorts.
The closer they are together, the quicker the rooms is covered in Steam, so it could be useful to try and keep them away from eachother.
Once the Steam is at max, they will be impossible to hit (only 5 % regardless of To Hit Buffs) so it is important to defeat them before it rises to that stage.