Prismatic Blade is one of the Spellblade Passives which is unlocked at level 20. Requires Mage level 20 and masteries unlocked.
Description
+1 dexterity per point.
Your lightning melee attacks deal 1 addditional lightning damage per point.
Your cold melee attacks deal 1 additional cold damage per point.
Your fire melee attacks deal 1 additional fire damage per point.