First of all I would like to state, unfortunately I cannot confirm this 100%, hopefully someone can back me up. (Heard this over vent)
When rotface casts Mutated Infection - Spell - World of Warcraft, the person targeted would run over to the entrance gate. It was told running into the gate while the infection goes off will cause the slime to be stuck in the middle of the gate. Thus eliminating slimes from the fight.
As I said I can not confirm this and I'm not too sure if this will stop slimes from merging either. All I heard was "Yeah me and *** we're bugging out Rotface last night. Running into the gate so the slimes spawned in the middle and got stuck."