Doors and keys

Normal doors
Normal doors have a certain amount of keys needed to open them. The amount of keys is indicated by the amount of yellow tiles on the door. When a key is collected the key will disappear and one of the door's sockets will change to an orange color.

Keys
Keys are used to change a door's key count (The amount of collected keys) by 1. When a door'skey count reaches a specified number the door will disappear.

Power doors
Power doors are opened when the player enters a certain range with a certain amount of power.

The amount of power you need to open a power door can be: