Realm-Scorcher Hellkite

Bargain refunds four mana of any colors, but only if the creature was actually bargained, so a six-mana spell arrives at a net cost of two and leaves fuel sitting in your pool. That refund is the whole play pattern: it wants to come down off the back of a token you no longer need, a spent artifact, or a lapsed enchantment, and it wants a spell waiting behind it to spend the leftover mana on. Because the four mana comes only from the bargain, the deck has to keep a stream of expendable permanents flowing rather than hoarding them; that conditional is what stops the refund from being a flat discount and turns it into a tempo swing you have to build toward. The rest of the frame is deliberately conservative for a haste flier: a 4/6 body outlasts most sweepers a 4/4 would fold to, and the repeatable pinger converts spare mana (including the refund itself) into reach, spot removal, or incremental damage to the face. Bargain rewards exactly this construction, where the sacrifice cost is worded broadly enough that the deckbuilder decides what counts as disposable, and the Hellkite is the mechanic's most ambitious payoff: not a cheaper Dragon, but permission to cast the Dragon and then keep casting in the same turn.