Wilykit and Wilykat find a magic harp containing a genie. His name is Charr-Nin.
Mumm-Ra offers to free the genie if he helps to destroy theThunderCats. Foolishly, Charr-Nin agrees, and begins trapping the Thundercats in his lamp one by one. Mumm-Ra's plan works, and he betrays Charr-Nin.
During their arguing, the Thundercats manage to escape, leaving Mumm-Ra and Charr-Nin battling beneath the earth.
That harp always freaked me out as a kid