These elementals come as part of a multi-pull involving Magical Horrors. They should be tanked or Banished or trapped until the group is ready to kill them. They are vulnerable to Fear and Stun and cannot use their Warp Breach ability when not in control. As such, carefully timed use of such abilities can prevent the detonation. A rogue using Kidney Shot before the Mana Warp begins to cast Warp Breach will prevent the explosion damage. It's a good idea to stun these at about 8-15% of their health, depending on the length of the stun.