Riptide Mangler

The body comes out as a 0/3: nothing stops it from declaring an attack, but at zero power it deals no damage, so the creature sits inert in combat until you pay to arm it. The ability is where the design turns strange. Most blue power-manipulation drains or shrinks the target; this one leaves the opponent's creature untouched and simply borrows its number. Point it at a 6/6 and you have a 6/3 attacker for the cost of an activation; point it at your own fattie and you can re-arm the Mangler again later, since the change lasts indefinitely rather than wearing off at end of turn. What complicates the math is that the new power locks at the moment of activation: copy a 5/5, then watch that creature get pumped to 8/8, and the Mangler stays a 5. It tracks a snapshot, not a live value. That snapshot turns the card into a timing puzzle rather than a finisher. You are activating to catch a creature at its biggest, and an opponent holding a combat trick can let you commit to a number, then pump past it and leave you smaller than you paid for. The toughness never moves off 3, so no matter how large the power climbs, the Mangler stays a glass attacker, lending itself a body it can lose in any trade.