Her defining capability is a once-per-turn ability that triggers specifically when the opponent declares an attack
As for the actual effects of Ominous Harvest, its the perfect example of a modern combo piece: flexible despite its simple text box, and explosive power that starts strong and scales hard with the game length
Affinity An ability that reduces the cost of a spell depending on how many Equipment, Towns, orBirds you have in play
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
(b) only the Auctioneer may place a bid on behalf of the Seller
I'd want to play this in combo decks that win the game with infinite loops or Thassa's Oracle rather than standard combat damage