"When you draw power from demons, it's a good idea to have a backup plan in case they disagree."
Banish is a level 32 warlockcrowd control spell, usable only on Elementals, Demons and Aberrations. It prevents the target from taking any action, and also makes it invulnerable, preventing the target from being affected by attacks, heals or spells of almost any kind.
Damage over time effects applied to the target will continue to count down when a target is Banished, but cause no damage.
Recasting Banish on a target already afflicted by the spell will cancel the spell's effect.
Mobs can be taunted during a Banish. Communicate to your tank when the effect is seconds away from wearing off, they will appreciate the notice as it will allow them to place a taunt effect on the mob and keep it from running out of melee range.
As with other crowd control abilities, it can be useful to employ the "Focus" system.