Hearthpwn

Look, I think that Chromaggus is by far the strongest boss on heroim BRM. With thad said, lets be clear to say that you need some luck first few rounds to succeed.

I've tried almost every single deck shown to pass it and everything failed for me constantly and I feel that they needed too much luck to pull off.

The druid one was about luck and was missing a way to remove Chromatic Dragonkin.

Patron deck was close but health has gone too low until all patrons were out and u had to draw Kelthuzad to ensure vicorty.

Other priest decks failed for me and new TGT cards all I needed to complete it.

After TGT launche it was clear to me that with minor changes it's going to be a lot easier and after 4-5 loses i won it and the other times i was just missing 1 or maybe 2 cards to complele the game.

Gameplan:

Must draw until 2nd round - at least one Lightwell. always put both if possible.

Other good draws to start with:

1. Light of the Naaru - heal + advantage with a lightwell + hero power.

2. Mind Vision - with some luck get you'll get Chromatic Dragonkin which is amazing.

3. Shadow Word: Pain - you need to for an early Chromatic Dragonkin.

4. Silence - you need to for an early Chromatic Dragonkin.

5. Convert - Same with Chromatic Dragonkin. The game I won i didn't get it early but i used it to take his Alexstrasza and the Shadow Word: Death him. Used Alex the next turn to lethal. was pretty cool.

Look, the whole game againt him is about survival until round 6-7. If u managed to do it with some life on youre side you will win the game.

About his cards: Save green and red. that means that u can play round 3 as usual and put another lightwell, kill his Chromatic Dragonkin or buff the well . all the rest must be thrown since they can hurt pretty bad. double swipe on our well is very bad.

Chromaggus dont care about the Lightwell until it has attack. so don't inner fire it until u buff it with enough health to kill him. keep it healing you and survive. remember that you can draw cards with the cleric or buff his minions with Power Word: Glory.

About flash heal - I found out that sometimes u must Divine Spirit to Inner fire Lightwell early in the game to survive and eliminate big threats (BY THE WAY - ALWAYS TRY TO USE POWER WORD: SHIELD BEFORE DIVINE). If it happens you need to heal it to max health before using the next divine spirit so flash heal is useful in those cases and use it there. if u feel like healing urself to survive thats cool as well. make the good choice. 

If he somehow kills the Lightwell early try to Resurrect or start again.

If he uses round one coin + Chromatic Dragonkin and round two Chromatic Dragonkin again - concede and start again.