Festergut

Health:
10 Man: 9.412M
10 Man Heroic: 13.7M
25 Man: 40.44M
25 Man Heroic: 52.2M
Enrage: 5 mins
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Abilities:
-Gaseous Blight - The Gaseus Plague inflicts 2925 to 3075 Shadow damage to all nearby players. Instant.
-Inhale Blight - Inhales the Gaseous Blight in the room, increasing damage dealt by 30%. 3.5 sec cast, 15 sec cooldown.
-Pungent Blight - Violently releases the Gaseous Blight, dealing 48750 to 51250 Shadow damage to all enemy players, releasing the deadly Blight back into the room. 3 sec cast, 15 sec cooldown. [That is why you need to get under Gas Spore, which will target your immune system and give you shadow resistance (Blight Resistance)].
-Gas Spore - Unleashes a Gas Spore, inflicting 2-4 random targets with a gaseous spore. The Spore will explode after 12 seconds, inflicting 1950 to 2050 damage to all nearby friends. The damage from the Gas Spore builds the targets immune system, giving them a resistance to the blight. Instant, 18 sec cooldown. [On 10 man mods, 2 spores will be spawned. 1 goes to Tank and Mele Dps, other one goes to Range dps and healers].
-Gastric Bloat - Inflicts 14625 to 15375 damage and applies Gastric Bloat to the target, increasing damage done by 10% for 1.67 min and will cause a Gastric Explosion at 10 stacks inflicting massive damage to nearby allies. [Tanks requires switching before stacks get to 100percent]
-Vile Gas - Inflicts a Vile plague in targeted area, inflicting 4875 to 5125 damage every 2 sec for 6 sec. The plague causes the infected targets to vomit uncontrollably inflicting 3900 to 4100 damage to nearby allies. Instant. [Range DPS and healers, stay away 1 from another for 10 YARDS or just go and die...]
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https://www.youtube.com/watch?v=L_0n38eMJXU
http://www.downfallguild.org/Festergut
If you have any question, feel free to ask them below.