Fight Anger with Anger

1. proceed through the instance like normal until you get to the last room. there is a lower platform with three groups of mobs and an upper platform with the final boss and 2 mob groups, one up the left stairs and one up the right stairs.
2. kill the first group in the lower platform, and then kill the one on the right. make sure you get 20 stack on this group. the adds keep spawning until the mob in the middle is killed so it's not difficult.
3. kill the group of 3 big mobs up the right stairs on the upper platform, and then immediately pull the boss.
4. use the group of mobs on the left side of the upper platform to refresh your stacks. it is a group of 1 big mob and about 4 little ones. if it's normal mode, you might not even need it. if it's heroic, just assign one person to kill little mobs as needed. the big guy doesn't hurt much and you can kill him afterwards.

You get one stack of the buff every time you kill a sha of Anger (the small sha through out the instance) The buff stacks to 20, and each sha you kill you refresh the stacks to a max of 30 seconds.

When you get to the second last room (room with the 3 sha spawn points), kill the first group including the spawn point in the middle. Pick either left or right, does matter which, kill off the small Sha but leave the spawn point in the mid alive. You should have 20 stacks passively from killing this room. Go up stairs, kill trash.

Have a ranged, or heals pull the small sha so you always have 2-3 nipping at your heals throughout the fight then you wont have to go running to find one to kill. They dont hit for a lot and only have about 90k health, so easy to just pick one every 15 seconds or so and kill it to refresh your stacks. They will respawn at the spawn point in the downstairs room around every 20 seconds, so just keep pulling them up.

No need to rush this part, just make sure you keep refresing your stacks.

As a bonus 20 stacks equals 60% increased damage, so will help you get your heroic timer in the process.

We failed the timer at beating Abomination of Anger on heroic mode and did not get the achieve for killing him on our second try (same instance) with 20 stacks. When we queued normal mode, we received the achievement without issue. Heads up for anyone else who it may have bugged for.