Underlight Conjurer's Brilliance

2 pieces: (2) Set: Arcane Surge increases Spell Damage by an additional 10% and its duration is increased by 3 sec.

4 pieces: (4) Set: For every 3,600 Mana spent on and during Arcane Surge, your spell damage is increased by 1.0% for 18 sec after Arcane Surge fades, stacking up to 25 times. Mana regeneration is increased by 50% for this time.