How do you make a red coin challenge

I see it on videos and in episodes but how do you do it I know it has something to do with Events/Layers I would like to use these for my episode so please help :D

I've checked the invasion 2 Red Coin level (I don't renember the name of the level, so don't ask.) And the red coins were at the same layer.
I've tried to do so, but failed.
I checked events, and still failed......

1. Make the coins a layer for themselves and just them
2. Make a event that shows a star or whatever you want it to do when you collect the coins
3.Put the coins down labeled with the layer and all have the event in the "No more in the layer" NPC event section
4. Voila your done

thank you

Solved! LOCKED.