Minecraft Dungeons:Key Golem

The Key Golem, also known as Gold Key, is a small mob in Minecraft Dungeons which helps the player unlock doors upon collection.

Behavior
The Key Golem will start out asleep. When it is awake, it will attempt to evade the player at any point it can. The player has to hit it to collect it, at which point it gets strapped to their back. The Key Golem will squirm and yell while on the player's back. If the player manages to get to a locked door while the Key Golem is still with them, it will disappear, the lock will turn yellow, and then the door will open.

Trivia

 * There is also a Diamond variant.