Shadow Bolt?
It looks like you reflected its attack. Imps do a slow, high damage projectile so that kind of damage isn’t unreasonable.
It is the ennemy skill, imps shoot very predictable but powerfull projectiles, this one probably got reflected when you used Magnetic Shield and dealt critical damage.
If you used Staff 3, you likely reflected his own attack.
Maybe you reflected something with magnetic aura? Or you didn’t realize that you were actually playing WoW ^^
Rachat – Elementalist (Abbadon’s Mouth)