Skeleton Key

This miniature skeleton holding a knife has been carved out of a human’s vertebrae. As an action, you can use the miniature knife to self-inflict 2d4 damage that ignores all resistances and immunities. When you do so, the skeleton animates and walks towards the nearest locked door or object within 10 feet, then plunges itself into the lock and makes a thieves’ tools check (it has a +10 bonus) to crack the lock. Whether successful or unsuccessful, the skeleton then walks back to you and returns to its inanimate state.

Alternatively, you can use an action to cover the skeleton in blood. When you do so, the skeleton rushes to the nearest lock within 10 feet and unlocks it (as per the spell knock ) before dissolving into red mist.