This maze game has been adapted for school use from a lecture written by Carl Gustafsson.

To make the maze more interesting, we should be collecting diamonds along the way.  But we don't want to let the person move to the next level until they have collected all the diamonds.  Here are two ways we can make sure of this:

We will use the first method here:

Add 2 new sprites sprDoor and sprDiamond  You can use any suitable sprites.  These are the ones I used:

sprDoor: As the rock is only 24x24 pixels, I stretched it by 135% in the sprite editor to make it fit the grid better.

sprDiamond:  Make sure that your sprite is a suitable size; you can stretch or scale it in the sprite editor if you need to.

Add 2 new objects: objDoor and objDiamond.  Make the door solid as it acts like a wall.

Sounds

Add sounds for picking up the diamonds and for opening the door.  Call them sndDiamond, and sndDoor.

Place diamonds around your maze.

The objDiamond should have a collision event with the person.

It should then play the diamond sound and destroy itself.  (The destroy the instance action should be set to self)

 
Place the door so that it blocks access to the target.  Don't put any diamonds on the other side of the door!

In the person object, add a collision event with the door object, stopping the person and aligning it with the grid.  (Just the same as you did with the wall object.)

Go back to the door object.  When all the diamonds are gone, the door should play a sound and destroy itself. 

 
 
There is an event called a step event.  That event occurs once for every step of the game, which is usually 30 times a second.  It is very useful for things that should be checked often during the game.  

Add the step event to the door object. Add the 'If the number of instances is a value' action.  (On the Control tab) Choose these options:

We want to play a sound and destroy the door if there are no diamonds left, so we need to add block markers to our actions.  We need block markers so that both actions are carried out if the number of instances is zero. 

If you didn't use block markers, the sound would be played when the diamonds were all gone, but the door would be destroyed in the first step of the game!
  Your game should now be ready to play.  Save and play your game to test whether it works as expected.
 

The Target Marker

Instead of blocking the target with a rock, you could use a target that does not appear in the room until all the diamonds are collected.  We do this by placing an invisible target marker object in the room.  When all the diamonds are gone, it destroys itself and creates a target object in its place.

Create a marker sprite and object.  Call them sprMarker and objMarker.  Make it invisible by unchecking the Visible option.

Then use the step event and add an action 'If the number of instances (of the diamond) is zero,  Change the Instance to change the marker to the actual Target object.

Place the target marker in the room where you want the target to appear.

 

Now we will move on to look at scoring.