Full House (25 player)

just finally got this achievement, probably not needed, but anyway there are my five simple macros used for assurance. bounded 1-5 bottom left actionbar2, i didnt even remember the names represented by marks, so i didnt care which one still missing, just waited a liil bit more, then hit these macros again and as i saw five different marks, i knew Iam good to go :-p using single tar abilities as those fives have to remain until boss's death.

/cleartarget
/targetexact Reanimated Fanatic
/stopmacro [noexists]
/run SetRaidTarget("target",1)

/cleartarget
/targetexact Cult Fanatic
/stopmacro [noexists]
/run SetRaidTarget("target",2)

/cleartarget
/targetexact Deformed Fanatic
/stopmacro [noexists]
/run SetRaidTarget("target",3)

/cleartarget
/targetexact Reanimated Adherent
/stopmacro [noexists]
/run SetRaidTarget("target",4)

/cleartarget
/targetexact Cult Adherent
/stopmacro [noexists]
/run SetRaidTarget("target",5)

Just got this achievement in 25 man, and I will freely admit that I had no idea what was going on at any point in time during the entire six minute fight.

EDIT 8.3: Vayga's comment is accurate, the green circle mechanic etc no longer seems relevant, at least in Heroic 25. You can just aggro Deathwhisper to start the fight then stand in the middle of the room until there are enough mobs. Then kill her.

If you're having trouble with this, it may be because:

a. She isn't summoning mobs. This is because you burned through her mana shield.
b. You are killing all the mobs at the same time, thinking she's going to rez one into the new mob type you need for the achievement. She isn't, she transforms one that is still alive, after you kill one of that type in the green circle.

1. Whack Lady Deathwhisper to start the fight. After that, leave her in peace.
2. Deathwhisper will start summoning adds. Fanatics are melee. Adherents are casters. You need her to transform one of each type into a Reanimated Fanatic / Adherent. The system for proccing the transformation is the same for each, so let's take Fanatics as an example.
3. Deathwhisper casts a green circle on the ground. If a Fanatic dies in the green circle, and no other Fanatics are alive, nothing happens, and you will never complete the achievement. However, if a Fanatic dies in the green circle when there is another Fanatic alive outside the circle, then Deathwhisper will "reanimate" the living Fanatic into the mob you need. That's to say, she does not resurrect the dead mob, she transforms a living one (not really "reanimation".) This means, if you run around killing as many mobs as fast as you can, she will never have a living mob to reanimate.
4. These reanimated mobs are easy to identify - they're giant skeleton models. Obviously don't kill them (yet). When you have a Reanimated version of each, just keep the numbers of mobs down so you can see easily. Kill fanatics especially as you need one to transform into the Deformed Fanatic.
5. When you get the Deformed Fanatic (it's a large zombie figure), check you have a normal Fanatic and a normal Adherent alive also.
6. You can attack Deathwhisper and complete the achievement.