Wormhole Serpent

A 3/5 body reads as a wall, built to clog the ground and survive combat, but the activated ability turns that defensive posture into an offense: five to cast, then four more each turn to push a single attacker past every blocker. The math is the whole design. That toughness of 5 keeps the Serpent on the table combat after combat, so the ability can keep pointing at whatever needs to connect. The activation targets any creature, not just itself, which widens its job from self-evasive beater to escort: it can walk a poisonous attacker through, land a combat-damage trigger for a commander that demands one, or simply usher the biggest thing on your side into open space. Four mana per activation is steep enough that you rarely do it while also developing a board, so the Serpent earns its keep late, when lands are plentiful and one unblocked swing settles the game. It descends from a long line of blue creatures that trade a modest body for repeatable unblockability, a role blue has filled since the earliest sets without ever letting it come cheap. The price is the point: evasion this reliable is meant to cost a full turn's worth of mana every time you cash it in.