Doctor Klein is the second boss of the instance and requires a lot of movement. 

The strategy is the same for the Elite mode with the major difference being Doctor Klein's health is 278k HP and damage dealt is stronger.

Open the Void – Avoid the motes on one side of the bridge
Wave of Mutation – LoS using the broken pillar at the entrance to the bridge
Swell of Mutation – Avoid the wave attack down one side of the bridge

Open the Void – Opens a portal which emits Motes of Aten down one side of the bridge
Profane in the Membrane – Magical attack
Wave of Mutation – Wave attack down the middle of the bridge, need to LoS
Swell of Mutation – Wave attack down one side of the bridge
Relentless – Buff causing Hinder and Impair abilities to last only 33% of their duration on this boss, and the boss will become immune to CC if too many are cast in rapid succession

Spawned adds:
Motes of Aten – Summoned by Open the Void, will silence a player and if the mote is not damaged by other players (forcing it to release), it will cast Dream's End causing the silenced player to instantly die

The first time you encounter Doctor Klein, he is on a bridge with a broken pillar lying at the entrance.  Be careful not to fall off the bridge during the fight.

The tank should take Doctor Klein where he stands.  When he casts Open the Void, a portal will open on one side of the bridge and emit a stream of Motes of Aten.  As in the first boss fight, these need to be avoided or they will silence the player, requiring the other players to damage the Mote until it releases, or else the Mote will cast Dream's End and instantly kill the silenced player. This is often cast down one side of the bridge, then the other, requiring players to move back and forth.

When the boss casts Wave of Mutation, everyone needs to LoS the ability using the broken pillar at the entrance to the bridge.  Wave of Mutation is a wave attack down the center of the bridge, and the only safe spot is behind the pillar.  This attack deals significant damage and can mean instant death.

Swell of Mutation is a similar wave attack, but only on one side of the bridge so it can be avoided.  This is often cast down one side of the bridge, then the other, requiring players to move back and forth.

Once the boss reaches about 45k health, he has been defeated and will make his exit.