Ghoul

That would be really cool, like the zombie Geonosians from Star Wars.

It would be great to get some more undead minifigs and sets. As long as the undead don't look like the skeletons from Ninjago, those were a little blocky. I would be happy with some new skeletons, zombies and necromancy stuff.

I Imagine the villians theme being newer versions of the old Insectoids sets. The Insectoids could be remade to be like the Borg from Star Trek. They have a hive mind and want to assimilate people and technology, or infect the Nexo Knights minds and technology in this theme. They even share the same colors of black and green. I'm guessing poison powers (poison their minds) or toxic potions are used for "infecting". Seems like a promising year for Nexo Knights.