Gigantomancer

The repeatability is the whole trick. Most effects that set a creature's base stats to a fixed value fire once and resolve: a pump spell, an enters-the-battlefield trigger, a one-shot. Here the ability is a one-mana, instant-speed switch with no cap on activations, and it points only at creatures you control. The use that follows from that is going wide-then-tall: a board of irrelevant 1/1 tokens becomes a row of 7/7s, one mana at a time, until you run dry. Because it sets base power and toughness rather than adding to them, it overwrites whatever the creature already was, so the size of your smallest token and your fattest beater converge on the same number for the cost. That overwrite is the mechanical subtlety worth knowing: it lives in Layer 7b and applies before +1/+1 counters, which still stack on top of the new base, so a counter-laden creature can climb past 7 even after you resize it. The shaman's own 1/1 body is what you pay for the privilege: it dies to almost everything and does nothing the turn it lands unless you already have targets worth resizing and the mana to do it repeatedly. The idea is older than the rate suggests: a mana sink that does not generate value so much as redraw your own board, over and over, for as long as you can pay.