Thanks for your feedback.
Correct, you can only bring 1 key.
In early design I try create like only 1 combination that can bring you move to next room. And each level will increase number of false key or door. And I didn't make it random generate labyrinth.
In current design I want to make it random generate labyrinth. But I found it really difficult to play in higher level, first you need search a path, and found correct key (you didn't know which one is correct key), looking for correct door and avoid ghost. That when I make it only 3 key and 3 door, you can use 3 combination to move. And I change into color key from number key, so player can look from far away. That why I use only 3 (RGB).
But I like the idea using 2 key to open the door, like purple door need blue key and red key.