Discard, of course
You may not get that much value back for each sacrifice individually, but thats a lot more than the zero value most decks are getting in these scenarios
KALDHEIM Burning-Rune Demon Burning-Rune Demon is a card Ive never seen anyone talk about, let alone cast, and I cant say Ive read a decklist that includes it, either
While most players preferred Dragonlord Ojutai as part of the squad, Shota went with Icefall Regent instead in order to stay just U/B
(6/6/2025) To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as a flashback cost), add any cost increases (such as kicker costs), then apply any cost reductions (such as that of The Water Crystal's first ability)
Card advantage that rummages and wheels like Unexpected Windfall and Imposing Grandeur are your best friends, both to fill the graveyard for cost reduction and to make sure you have enough cards to reliably trigger Eris