Grenzo, Crooked Jailer is a rare Legendary Creature — Goblin Rogue card from Alchemy: Outlaws of Thunder Junction (YOTJ), collector number 22.
When Grenzo enters and at the beginning of your upkeep, heist target opponent's library. Once each turn, you may pay {0} rather than pay the mana cost for a spell you cast that you don't own with mana value 3 or less.