That 6 Nimble door lock requires an absurd amount of grinding to pass, even with the shortcut to spawn an enemy. -_-;

I'm assuming you mean the door in the Abandoned Laboratory still. That door is designed for you to find out that you can change your mood, and that the mood affects your stats. In the same tile as the door, there is a separate interactable to the left, The Jigsaw Puzzle. If you solve that, it will boost your nimble up enough for you to unlock the door without any grinding.