Gem of Knowledge

Helm of Champions/Stormcrown: (Passive) Grants a 10% chance on attacking to create a storm at the target's location, dealing 60 damage per second for 8 seconds
Circlet of Mana/Tiara of the Stars: Teleports the hero to any visible position on the map. The hero will be teleported back to its original position after casting a spell or when 3 seconds elapse. 90 second cooldown.
Plate Helm/Templar's Helm: Nearby enemy units with a buff take 15% of their max health in damage. The hero will be healed from 50% of the damage done. 60 second cooldown
Executioner's Hood/Adjudicator's Coif: Passive: Gains 20% extra experience.
Dragonscale Mask/Guise of the Witchdoctor: Turns 10% of the hero's current health into twice of that in mana. 15 second cooldown