the thundercats cannot ever truly defeat mumm-ra
 

mumm-ra the everliving is immortal and cannot be destroyed. only banished or captured but he would survive. he cannot be killed in battle either. the thundercats are mortal, they age and die eventually. the thundercats i guess would continue to battle mumm-ra until they no longer can do so or defeat him temporarly. mumm-ra told them once in the 80s series he stated that the thundercats were the intruders on third earth where he has lived for 1000 years and they disturbed his rest and says but i have time 1000 years more 5000 you cannot defeat me for i am mumm-ra and wherever evil exists mumm-ra lives, mumm-ra lives, mumm-ra lives. then he laughs and disappears. so in the end they cannot ever truly defeat mumm-ra the ever living......

That's part of the reason he's such a cool bad guy!

They should let the bad guys win once and a while. There's nothing more exciting than when the good guys have to work harder to overcome a powerful villain. It's what made Vader more kickass in Empire, Apollo Creed in Rocky and why the pilot episodes of the new Thundercats were so awesome.
I was hoping that Mummra would fly away with the Book of Omens and I was also hoping that he managed to own the eye of thundera for a little while and made the Leo storyline a side story once and a while.
When the bad guy loses all the time they become somewhat of a joke.