Obviously not a great card unless you have Ethereal cards in your deck, but if you do this is worth grabbing. It's particularly strong against multiple enemies, but even in single enemy fights, dealing 33 or more damage for 1 or 0 is very worthwhile.
It's a little tricky to get the discount going initially, but the payoff here is massive. Combine with a good draw engine to keep drawing it at 0-cost.
Summon 6. Exhaust.
Deal 33 damage to ALL enemies. Costs less for each Ethereal card played this combat.
Deal 8 damage. Apply Doom equal to damage dealt.
Summon 5.
If Osty is alive, he deals 9 damage to ALL enemies and you gain 9 Block. Osty dies.
