Key Death

A Key Death is a situation in Super Mario Maker where a key that opens a door doesn't get saved once obtained if the player dies, literally, the player dies with the key.

For instance, given the circumstance that a player collects a total number of red coins to obtain a key, the progress that the player makes while obtaining them can be saved through checkpoints, but once the key is obtained, the game does not allow the player to respawn the key once they revive after dying, losing both the key and the progress made through the coins, making the player have to recollect the coins once again.

Key deaths are an inherent risk to the game itself, as the player can always die regardless of having obtained either the coins or the key itself due of the nature of the game, but key deaths can be used as a troll element as well, creating a situation where the player loses all their progress.