Echo of Eons

Timetwister's descendant, reworked to solve the problem that has always dogged its lineage: the symmetry. A raw refill of hand and graveyard back into the library hands your opponent a fresh seven too, which is why the effect only ever mattered to decks positioned to spend theirs first. Flashback rewrites the calculus. The graveyard cast is where the design actually lives: you never have to draw this card at all. Pitch it early or mill it into the yard, then buy back the shuffle-and-draw for a fraction of the front cost, converting a spent hand into a full grip on a turn you have already committed to going off. That turns a fair-looking six-mana sorcery into an enabler for storm-style engines that empty their hand and then reload it cheaply, treating the hardcast as pure setup rather than the payoff.

The exile clause on flashback is the ceiling. One replay and the card is gone, so this is not an infinite loop by itself; it is a two-shot burst that asks a combo deck to have the rest of its pieces assembled before the second casting fires. That constraint ties the card's power to the deck built around it rather than to the card in isolation, keeping it an enabler instead of an unbounded engine. The reason it reads so much stronger than the plain sorcery text suggests: the decks it belongs in do not want to hardcast six mana for seven cards. They want to shuffle away an emptied hand and buy a fresh seven for two and a blue.