Sacred Excavation

Regrowth with a keyword tax attached. The effect only reaches back for cards that carry cycling, which sounds like a limitation until you notice what it is really doing: cycling is a mechanic built around velocity, cards designed to be shed cheaply and swapped for fresh ones, and this hands you a second lap on that discard fodder. Buy back two of them at once and you have converted a keyword about digging quickly into an engine about grinding long. The targeting requirement is what keeps the two-for-one from being free: everything returned has to share that single keyword, so in a deck that never cycled a card the spell does nothing, and in a deck stuffed with cycling lands, cycling creatures, and cheap cycling filler it refills the hand with the exact pieces you already spent. That dependency is the entire pitch. Blue could regrow any spent spell; instead the effect is walled off behind a deckbuilding commitment, so a four-mana double-return never becomes a generic staple and stays a reward for leaning all the way into a cycling shell. You pay for the recursion in synergy rather than at the counter.