I’ve done two of these challenge modes so far and without seeing the others I’m pretty sure the frost mage is hands-down the most over-tuned.
For instance I did the disc priest one, and although I had to tweak my talents for a quicker interrupt, I didn’t do much else. Sure it was difficult but after maybe 5 tries I got it.
As I recall I had to tank the main boss while his wyrm was spitting at me, which meant healing myself while doing damage. Yes, disc priets heal while damaging but managing mana was a bit of a problem. He did a strong damage ability every so often which I could only interrupt once and had to tank the next attempt before I could break it again. I think I also had to look out for spikes coming out of the ground and deal with some adds. Wasn’t too bad but after the main boss died I had to also kill the wyrm and I was low on health and mana at that point.
Frost mage, good gosh. It starts off with a paladin named Karam chasing you. You HAVE to keep him slowed because if he gets in melee range, he either one-shots you, or he does so much damage you are going to lose. That means keeping him chilled and slowed constantly and it’s best to NEVER snare him because he’ll start running after you if he gets too many stacks of “wasn’t kept frozen” or whatever it’s called. He also drops or creates purple circles on the ground you have to avoid because it slows you. Once he hits 34% health his brother Raest banishes Karam who heals back up (cheater) and summons slow moving adds. If the adds hit you, you’re done. You need to put enough damage into Raest while constantly Blizzarding the adds to hopefully keep Frost Orb constantly up.
When you damage Raest enough, he goes immune (cheater!!) and Karam starts chasing you again. While the adds are also chasing you. While a Hand from Beyond starts slowly casting a spell that will kill you. You have to keep Blizzard on the adds while also kiting and slowing Karam and the adds, while interrupting the first cast from the Hand and killing it before the second cast.
When Karam gets low enough again, Raest joins the party (of the slow moving adds, of Karam, and the hand) by summoning a circle you HAVE TO STAND in until it disappears or a GIANT FAST MOVING MOB spawns and kills you. So you have to kite Karam, kite the adds, keep blizzard going on CD, keep orb up constantly, deal with the hand, while standing in the circles, while also killing Raest.
I did get Raest to 12% last night though. Besides that other stuff, it meant that I had to create a special set just for haste (30%, 35% recommended), had to eat Bear Tartar to help with the kiting, had to pop hero and potions on the second phase, had to macro my counterspell specifically to the hand (because you have no idea where it’s going to spawn each time) and set up target macros for the brothers to quickly target them in all the mess. That literally meant replacing normal spells with new functions. People also recommend specific legendaries to even get it done reliably.
Sorry but that’s over-tuned.