Transformers: The Headmasters - Season 1 Episode 13 Head On, Fortress Maximus

In the city of San Francisco, a giant man-eating plant suddenly springs from underground, causing mass hysteria and major damage. In response, Ultra Magnus sends out the Technobots, Aerialbots and Trainbots to assist, but they are met by Bruticus, who battles Raiden. Ultra Magnus contacts Fortress and the Cybertron Headmasters, who then head toward San Francisco. They get beaten up by the plant, mocked by the Destron Headmasters, then another plant shows up, as well as another at the Witwicky house. Menasor then battles Computron, while Bruticus takes on the Aerialbots. One of the plant monsters is actually able to walk, and it attacks the Cybertrons' earth base, while the other attacks Fortress' battle station. Fortress then uncovers his sword of power and the base suddenly transforms into a giant robot, Fortress Maximus! He manages to destroy the plant monster, causing the others to blow up.