A Guardian is a strong UMA that guards a Forest, which will only appear when King Corobo accepts a corresponding quest from his Suggestion Box. When defeated by Corobo, the Guardian's Forest becomes a new town or city in the Kingdom of Alpoko. Most Guardians are larger, more powerful versions of regular UMA; however, the Owl Hag, Ogre Ergo and Blue Dragon only appear as Guardians.
If Corobo leaves the arena when fighting a Guardian, then the fight will end, displaying the message "Run Away!" and upon returning to the fight, the Guardian will have its health restored.
The Guardian Battle theme is a percussion-heavy rendition of Rossini's "William Tell - Overture", with a slightly reduced tempo.
- Cow Bones
- Mush Bro
- Onii Man
- Clockwork Knight
- Ogre Ergo
- Owl Hag
- Mush Geezer
- Blue Dragon
- Every Guardian has a hint towards their presence in their respective forest before their Rumour quest is accepted, with the exception of the Onii Man who lacks such a quest. Cow Bones has his skull lying on the ground. Yvonne can be seen swimming in the river. The Clockwork Knight has a statue of itself (which turns into the Knight). The Owl Hag's red eyes can be seen peering out of her house. Ogre Ergo has his mask and cleaver lying on a stump. The top of the Mush Bro, Mush Geezer and Radeeze are all sticking out of the ground, and the Blue Dragon has an Ice Crystal covering its lair.