How do you get the key sword in castle crashers

In the Industrial Castle level after Pipistrello's Cave, there's a large enemy with the Cardinal Animal Orb. The Cardinal finds secret hidden items. With the Cardinal go to the Full Moon level after Medusa's Lair. The Cardinal will find and give you the key in the second hut just before you go to the Snow World Level. The Key Sword opens the last door in the Animal Ark and unlocks the Berserker animal (he gives you a magic boost).