Mikaeus, the Lunarch

The body that scales itself, then pays itself out across the board. The X in the cost is the whole calibration: dump everything and he arrives as a fat lord-in-waiting, or pay just for a 1/1 that grows a counter per turn off its own tap. What makes the design sing is the conversion ability, which launders his own size into a team-wide pump. Every counter you peel off shrinks him by one and inflates everyone else, so a wide board lets you trade a single large body for a permanent anthem distributed across the whole team. That last clause matters: these are +1/+1 counters, not a temporary buff, so a board wrath that misses your creatures (or a damage-based sweeper sized to the old toughness) leaves the pump intact. The tension built into the design is that both abilities cost a tap and pull in opposite directions: a turn spent growing him is a turn not spent feeding the team, and vice versa. He is also a counter-doubling magnet, since anything that copies or multiplies +1/+1 counters turns the second tap from incremental into explosive. The result is a go-wide payoff that doubles as a mana sink, a creature whose printed 0/0 body is less a stat line than an empty reservoir you fill at the moment of casting.