Riptide Shapeshifter

Tutoring with a guarantee of resolution, paid in tempo rather than card advantage. Most library-digging effects of its era either fetched to hand (where the creature still had to be hardcast) or named a single card outright; here the cost is a five-mana body you have already committed, plus four more to crack it, in exchange for slamming a creature onto the battlefield. The crucial subtlety is that the "any creature" promise is only as wide as your willingness to thin the well: you name a type, then reveal until you hit one, so the search is most reliable when exactly one creature of the named type sits in your deck. A lone off-color bomb is not a liability but a homing beacon: name its type, hit it, done. Run a dozen creatures sharing a tag and you take whatever surfaces first. That makes this a converter more than a toolbox, and the reveal-and-put-onto-the-battlefield clause is what gives the conversion its edge: it ignores mana cost, so a 3/3 plus mana becomes something that would cost far more or never wants to be cast at all, and the put-into-play step dodges counterspells and every "whenever a creature is cast" trigger on both sides. The Shapeshifter line in its type box is mostly incidental: lacking changeling, the sacrificed body shares the named type only on the rare occasion you point the ability at Shapeshifters themselves, so the cost is seldom a partial refund of the search.