Prominent aristocrats like Carrion Feeder, Falkenrath Aristocrat, and Korvold, Fae-Cursed King become quite large as a result of their sacrificing abilities
Instead of drawing energy cards from your deck like in the original card game, one energy is generated for you to use on any of the cards that you currently have on your bench or in your active slot
Its one of the famous Alpha boons, and it helped to define the idea of fast mana in black decks
Reckoners Bargain is a newcomer on the block, and while many will instantly favor Deadly Dispute for the Treasure, theres a bunch of decks where Id be happy to take Bargain first
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 Fire Crystal's first ability)