Dorodoron

Dorodoron is the third of the Dark Fall to attack Earth. He's an arachnid-alike creature that travels underground instead of through the air. Dorodoron transforms earth-related objects such as rocks and cobblestones into Uzainaa monsters. He also occasionally takes commands from two suspicious girls (Kaoru Kiryuu and Michiru Kiryuu) that are in the same class as Mai and Saki. His name comes from the word "doro" which means "mud" in Japanese.

(Source: Wikipedia)