I have a pretty solid win rate with a custom Carapace deck (32-8 or 80%). It's basically just a random collection of good cards: some Thrive, some Deathwish, some Organics. Both "The Aparian Phantom" and "The Beast" are great in this Seasonal mode, and "Keltullis" can always wreak havoc against any kind of swarm if he's left unchecked. Truth be told, I'm little surprised that my deck is doing as well as it is; although, I still lose every now and then, mainly to NR/SK players who actually have optimised decks and know what they're doing.Personally, a lot of fun on the seasonal modes is finding which factions are popular and trying to beat them with the other factions.
For example, this seasonal, NR and SK clearly dominate, with SY also being quite strong, so using ST or NG is quite interesting and i applaud anyone who also does it. I didnt even mention MO because its just awful in this seasonal, if anyone can pull that off please teach me.