142 cards found matching energy cost is 3

Galio, Indefatigable
Gemcraft Seer
Grim Apothecary
Guards!
Gustwalker
Heart of Dark Ice
Heimerdinger, Inventor
Heroic Charge
Hextech Anomaly
Hextech Gauntlets
Hunter's Machete
Immortal Phoenix
Insightful Investigator
Invert Timelines
Iron Ballista
Janna, Savior
Jinx, Demolitionist
Karthus, Eternal
Kinkou Initiate
Kog'Maw, Caustic
Kraken Hunter
Last Breath
Last Rites
Last Stand