Digimon Adventure:

Mugendramon was one of the Dark Masters and in control of the Metal Empire.

Digimon Xros Wars:

Mugendramon is summoned by Lilithmon to break the barrier of the Pyramid of Revival. During the fight with Shoutmon X4K and Baalmon, it changes to HiMugendramon. In the end, it is defeated by the combined force of Shoutmon X4K and Beelzebumon.