It seems that I’m getting a fair bit of traffic from people searching for tactics on how to get past the trash straight after the Flame Leviathan in Ulduar. So because of that, I’ll give a quick post on how our guild did it. This may not be the best way to do it, but it worked for us.
Even in the 10 man version, you should have 2 tanks. Have the tanks tank them where they stand but take them to either sides of the walls so there’s an even bigger gap between the two tanks. Have a healer on each tank standing at max range. The debuff jumps from player to player if they are standing within a certain distance. This means that if it jumps from the tank to one raid member who’s standing near the rest of the dps, it will spread. Just keep the dps and healers at max range from the Molten Colossi so as to not to get the debuff and will mean the tank should only get one application of the debuff and your healers shouldn’t have any problems. I do recommend that you pop cool downs to dps these guys down as quickly as possible.
A side note: If you only manage to kill one and then wipe, the one you killed will respawn again. This means you need to get both of them down in one try. Also, to get rid of the debuff from jumping about in your raid after they’re dead, you can either wipe, or stay alive long enough through clearing more trash and get into the water either side of Ignis’ room.
I hope this helps and good luck!