In lower power brackets, Kefka can work as a combo enabler for Waste Not, an enchantment that makes its user create a 2/2 zombie token every time an opponent discards a card, which can be every time that Kefka attacks or enters
Your sideboard consists of anything else you have opened (in Sealed) or drafted (in Draft)
It is arguably the most metal piece in the games history
Yuriko, the Tiger's Shadow and Gwenom, Remorseless both let you cast whatever your put on top, with the former doming your opponent for what is hopefully a ton and the latter acting as a Bolas's Citadel on a stick, essentially putting into play everything you tutored with Dreams and potentially assembling a game-winning combo, like this one, maybe
If you make a card that should be a common, you should have the design sense to do that
That Vehicle then becomes an artifact creature until end of turn