Ep 56. The Dream Master

Mumm-ra transforms himself into the Dream Master, and gains the power to control the Thundercats' dream selves. All except Lion-O. They all become slaves to Mumm-ra the Dream Master in their sleep, but when they wake up, they are just tired. However, when the Thundercats sleep again, Mumm-ra captures their dream selves in little bottles, and when Lion-O tries to wake them up, he can't. He goes and fights Mumm-ra, and frees the other Thundercats' dream selves. They wake up, come running, and help to defeat Mumm-ra again.