This is an interesting idea that popped into my mind. You how reimagined series like to differ themselves a lot from there original counterpart, but like to use things from the original. I don't know if this had been talked about but I was thinking what about using villains from the original Thundercats show. I know so far we've seen Mumm-Ra (A must), Slithe (of course), and Grune (not dead, and much more used).
Like how about the other mutants (Jackalman, Monkien, Vultureman, and Ratar-o). You don't have to make them deadly, just forumable enemies to the Thundercats.
Or what about those underused villains (or one's that were seen in more than an episode) such as Hammerhand and the Bersekers. Heck I'd like to see Pickpocket and Captain Cracker on this series. Although If they wanted to use the Lunatacks from the original series I think they should wait a season or two. They might seem silly, but in the hands of anyone anything can be deadly.
Just a thought that encoed in my mind.
Anyone have any thoughts? I have no idea how they are going to approach using the villains from the old series (aside from the three I mentioned, although Slithe doesn't talk much).