Most fights that require dispels, Blizzard is usually kind enough to make it a magic effect so all healing classes are able to dispel. However, Blizzard threw us the Horridon curve ball in Throne of Thunder.
There has been some confusion over dispelling this fight because there are multiple debuffs that need dispelling, and not all healers are capable of dispelling each one. There is nothing like getting yelled at for not dispelling diseases when your class is only capable of doing curses or poisons.
This fight has been a stumbling block for many guilds, particularly slightly undergeared or less-than-ideal raid comp 10m groups, hopefully this will help clear up some of the confusion over how to handle all the dispelling on this fight.
Here are the various debuffs and how you can dispel them, along with priority of most painful debuffs to least painful (although depending on your particular raid comp, venom bolt and deadly plague can be equally painful).
Note: Click here for the complete Heroic & Normal Horridon Healing Guide
Venom Bolt Volley (2nd door)
If the venom bolt volley isn’t interrupted (Gurubashi Venom Priests and Venomous Effusions both cast this), it applies a debuff to targeted raiders. This debuff is a poison effect. Druids (Remove Corruption), Paladins (Cleanse) and Monks (Detox; Revival) can dispel this. This is a stacking debuff, ticking damage every three seconds for one minute. You can also dispel the raid using Detox at the end of the phase.
You can pre-mark the venom-priests for interrupts, assigning an interrupter for each one to help with the amount of poison going out.
Deadly Plague (3rd door)
This is a disease effect which lasts for 5 minutes on the target. Paladins (Cleanse), Priests (Purify) and Monks (Detox; Revival) can remove this. A resto druid can also symbiosis a pally to get Cleanse and help dispel (Bonus tip: You can symbios a pally outside of raid and still use it inside).
However, one great way to combat this is to have your DKs save army for this phase, as the Risen Drakkari can target each mob in each army for the plague. Time your armies out, if you have more than one, so you don’t get overwhelmed, so make sure your DKs know the order of their armies. You can also use earth elementals to help, since the diseases are applied when the Champions and Warriors melee a target. Raid stacking up and using slows can help keep them off range.
Also, some classes with immunities can self-dispel with things like ice block and greater invisibility.
Blazing Sunlight (1st door)
This is a magic effect and ALL healers can dispel this debuff.
Stone Gaze (1st door)
All healers can dispel this stun.
Oh, and think Blizzard will balance healers in LFR so there is at least one healer capable of dispelling? Think again, I have been in groups that couldn’t dispel Deadly Plague in LFR.