Deathfire Grasp Reworked!
So, Deathfire Grasp was a great concept of an item, allowing mages/ap assassins to situationally burst down tanks, but it was poorly implemented, being more effective against squishies than tanks. I came up with a new version, specialized in dealing with tanks.
Deathfire Grasp (3100g) +100 Ability Power +10% Cooldown Reduction Unique Active: Deals 10% (+1% per 50 AP) of the target's Bonus health as magic damage. You gain +75% Bonus Magic Resistance Penetration against the target for 5 seconds. (100 second cooldown).
Affecting only bonus defensive stats means that this item would have little effect on squishies and quite the larger effect on tanks. Feel free to suggest changes if you feel the item may be too weak or too strong.