Demonbuff

The boards you make with this get out of control very quickly.

For the mulligan, fill your hand with as many one-drops as possible. You can keep a buff giver, or two different ones if you're paranoid about one of them getting banned, but keeping two of the same type is pointless, since you'll draw into them before you need them.

When on the coin, use it to summon Imprisoned Scrap Imp on turn 1, or Void Analyst if you don't have it. When not on the coin, you can probably pass turn 1, unless you know your opponent's deck will punish that hard.

For turn two, play Void Analyst. Then on turn 3, you should ideally have +4/+4 from the Scrap Imp awakening and trading away your Void Analyst. Now play your 1-drops.

The best ban is probably the card that slows down your opponent the most. Banning cheap AoE can also be good, but you can instead play around that by doing more buff rounds before playing your 1-drops.

For some reason, most of my opponents ban Voidwalker, which I don't think is the most important card.