Marble Titan

A continuous-effect Kismet pointed at power instead of permanents entering tapped, and the threshold is what makes it interesting. Drawing the line at power 3 or greater is a deliberate carve-out: it leaves the small attackers (tokens, weenies, mana creatures, utility one-drops) free to operate, while the fatties (the very creatures a defensive white deck most wants to neutralize) get walled. An opponent's 4/4 can swing once, then sits tapped indefinitely, no longer a blocker, no longer a second-strike threat. That asymmetry rewards a controller who keeps their own board under the line or who never needed to attack in the first place. It is a Pacifism that scales: instead of locking down one creature for one card, it walls the entire top end of a board with a single body, and unlike enchantment-based removal it cannot be answered by killing the affected creature, only by killing the Titan. The friction is built into the card itself. As a native 3/3, it falls under its own clause: attack with it and it will not untap, so the lockdown body is also a one-shot attacker that wants to stay home and hold the rule in place. That, plus the absence of evasion or protection, makes it fragile enough that any removal spell ends the lock cleanly. The design sits in that older school of white prison pieces that ask the table to play around a static rule rather than answer a threat, a lineage that runs from Winter Orb through Static Orb and the various untap-denial permanents that followed.