Guardian Archon

The hidden-information wrinkle is the whole reason this exists. Most protection in white is declared openly: you name a color, or the effect blankets everything, and the table adjusts around a known answer. Here the choice is a specific opponent, committed face-down as the creature enters, so the pilot buys a one-shot bluff whose target no one can confirm until it's cashed in. The threat of the ability constrains the whole table at once (any of them might be the chosen player), which is where the concealment does its work: opponents have to route their attacks and removal around an unknown, weighing whether they're the one this blade is pointed at. Timing is the other half. The reveal fires at instant speed and grants protection until end of turn, so it can be held up as insurance against a targeted removal spell, a lethal alpha strike, or a combat blowout, covering both you and a target permanent you control. Since protection from a player blanks that player's targeted spells, damage, and blocks, the opponent who was betting on getting through gets nothing. But cashing it in is loud: "Reveal the player you chose" turns the guess public, and everyone learns instantly who was and wasn't marked. That "activate only once" clause is the tax that pays for the concealment: it's a single trump card, not a repeatable shield, so the flying 5/5 has to carry the rest of the plan alone. A design built for the free-for-all, where secret information scales with the player count.