New AP burst item

Basically as an AP counterpart to the new assassin dagger

Build path: + + total cost >3k (like the dagger) Stats: 110 AP, +7% Movement Speed, + 10% Cooldown Reduction, and Duskbringer

Duskbringer: Hitting a champion with 3 unique spells (only 1 count per spell, so as to avoid more thunderlords fiascos) applies 1 stack of "Duskbringer", whereby hitting a 4th spell will detonate to deal 25% missing HP as magic damage.

Obviously numbers would be subject to change but you get the idea.