Stuffed Bear

Left alone it is an inert object: no toughness for combat to catch, no body for a sweeper to find, invisible to the creature-targeting removal your opponent has stranded in hand. The two-mana animation is the toll you pay to make it real, and it recurs every time, so this is a clock you feed one activation at a time rather than a permanent threat you can walk away from. Because the ability carries no timing restriction, it is not purely a your-turn attacker: hold the mana and animate it as a surprise 4/4 blocker on the opponent's turn, punishing an attack that assumed the board held no bodies. The catch is that animation cuts both ways. Once it is a creature, it is a creature for everything, including the instant-speed removal your opponent held precisely for this moment; the object is only untouchable while it stays an object. That puts it in the manland family of animate-on-demand permanents, but where a creature-land pays for flexibility with a slot in the manabase, this asks nothing but the repeated cost. The result reads as a patient grind piece: a removal-dodging body when idle, a mana sink when there is nothing better to do, and a green Bear artifact creature on demand for a shell that cares what its permanents count as.