According to Toys News International The Sub will begin this Monday 11th of January...
The Line-Up will be:
Mumm-Ra's weakened form as the Sub Exclusive.
These three we knew. What we didn't knew were the rest:
Heh! They went with Pumyra! I'm surprised they didn't go with one of the Tigers (Tygra or that lame ass Bengali) on year one... It's not a bad Line-up, but Jaga and Grune are basically KG and Hordak while we have 1 Mutant vs 3 Thundercats. Other than that it's pretty good. Wonder if the Thunderkittens will be their own two-pack.
You can get them here.
There is no end date to the sub yet, but don't dawdle... Mattel is most likely to have a month as the time window that the sub will be open. This means that you should get yours ASAP, just to be safe.