Sand Squid

The lockdown clause is the part doing the work here, and it runs on a self-imposed cost most players overlook: the tap effect lasts only as long as this creature stays tapped, and the "may choose not to untap" line exists precisely so you can keep it tapped indefinitely. That turns a 2/2 into a permanent jailer, frozen alongside its prisoner, holding down the opponent's best blocker or attacker turn after turn until something kills the squid. It is a soft removal engine masquerading as a creature: you trade your body's availability for theirs, and the better their creature, the better that trade looks. The islandwalk sits on a separate axis and only matters when the squid is free to attack; against an Island-controlling opponent it is an evasive clock, but it is mutually exclusive with the lock, since a squid maintaining a tap cannot swing. You pick a job each turn: jailer or beater, not both. That single-tasking is part of what keeps a repeatable one-creature lock from running away, and the rest is fragility. While it works, the squid does nothing offensive; it sits tapped, exposed to anything that targets it, and the moment it dies or gets bounced the locked creature springs free on its controller's next untap. It is a patient, almost janitorial design from an era when blue was happy to win by simply making sure the opponent's best thing never got to participate.