It would be unfortunate if the key fell into the wrong hands.

Key to the City

{T}, Discard a card: Up to one target creature can't be blocked this turn.
Whenever this artifact becomes untapped, you may pay {2}. If you do, draw a card.

The Brothers' War Retro Artifacts

{T}, Discard a card: Up to one target creature can't be blocked this turn.
Whenever Key to the City becomes untapped, you may pay {2}. If you do, draw a card.

"Presented to the Chief Artificer in recognition of his unparalleled service to Yotia."
—Rusted plaque

Commander 2021

Kaladesh Remastered

Activating Key to the City's ability targeting a creature that has already been blocked won't cause it to become unblocked.

Key to the City's last ability triggers during your untap step, but it's put onto the stack at the same time as abilities that trigger at the beginning of your upkeep step. Even though Key to the City's ability triggered first, you may order it before or after other abilities you control that are put onto the stack at this time.

You can activate Key to the City's first ability without targeting any creature.

You can pay {2} only once each time Key to the City's triggered ability resolves. You can't pay more to draw additional cards.