The Frozen Corrival

Level
will spawn as one level higher than the highest member of your group: (Level + 1)▲▲▲

Strategy

 * Knock the mob down to around 50%
 * When it AOE knockbacks and spawns 4 more mobs, stop attacking anything
 * roots itself but the new mobs move; back up to separate them
 * Sort through the new mobs until you find one with red background buff (the other mobs will have only a green background buff). Kill only the mob with the red buff
 * Killing the green buff mobs heals and resets the fight to the beginning - he will spawn the four mobs again at 50% health
 * Kill