Im most inclined to suggest a Voltron playstyle for Kefka, since both halves benefit from combat buffs, but honestly, you can build any deck around him
Thunder Magic Reds burn spells are nearly always the best commons, or at the very least in contention
With his doubling ability he makes some of the games strongest equipment even stronger as the various Swords of X and Y become just silly
I especially like how much control you have over when this transforms because it only triggers off spells that cost 4 or more, or you can put counters on the Emperor so you just need to trigger it once or twice to flip
Floodborn cards are ones that originally featured Storyborn or Dreamborn glimmers, but have been transformed by a magical ink flood, resulting in surprising character transformations and unexpected powers
Theres a chance some of these see reprints in the decks, no way to know till weve got the lists released