Cycloid (サイクロプス,Saikuropusu, Original version Cyclops) is a cyclops-like Bakugan equipped with a large hammer made of stone. In the anime, he is the Guardian Bakugan of Billy Gilbert.
Cycloid is a titan-like beast. He is incredibly strong, tough and eager for the fight. He has a single terrifying eye with a short deadly horn on his forehead and two vampire-like teeth. He finds humans both confusing and amusing.
Cycloid was found by Billy near the center of Bakugan Valley. Their debut was marked by a victory against another Subterra Brawler, Julie Makimoto. After a loss to Masquerade, Cycloid is sent to the Doom Dimension, along with several other Guardian Bakugan. Eventually The Top Brawlers are all reunited with their respective Bakugan. Cycloid is later teamed up with Gorem to fight against Tricloid, successfully defeating her. He also helps the Brawlers battle against Centorrior and Druman.