Ponder

The card-selection floor for blue combo, and the reason "one mana" and "fix your next three draws" being printed on the same card eventually drew a ban hammer in multiple formats. The structure does double duty: arrange the top three to set up your next two turns, then draw the new top card and pull the first of that arranged stack into hand. The shuffle clause is the part the engines built around it care about most. Pass on a brick and you wipe the slate; keep the order when it is good and you have sculpted draws three turns deep. That makes it not a smoothing spell but a deck-thinning, combo-finding, fetch-shuffling cantrip, and it sharpens the more your deck wants one specific card fast. Compare it to Preordain, which scrys and offers a more conservative dig, or Brainstorm, which buys three cards but leaves two on top with no shuffle of its own; Ponder both digs and resets in a single click. The cantrip clause is the leash: trading a card for a card means the selection itself is free, so the only cost is the mana and the click. For decks measuring success by how reliably they assemble a fixed line, that price has repeatedly proven too low, which is why Ponder has spent stretches of its life on banned lists in sixty-card constructed formats rather than in the maindecks it would otherwise dominate.