Slugterra

Eli Shane is determined to be the greatest Slugslinging hero of all. But in order to defeat the forces of evil, he must collect, train and duel with little critters called slugs, which transform into powerful magical beasts. Eli and his crew explore the caverns, challenge rivals and one another to friendly duels, and upgrade their gear in their underground world. But there is a threat to Eli and the slugs -- Dr. Blakk wants to transform the slugs into feral mindless weapons. No one has been able to stand up to Blakk's army of henchmen ... until now.