Hello, this question is kind of obvious for what will happen but anyway let's go to it:
There are currently 5 pit demon trophies. What differentiates them are their colors and their rarity. If you stack them on top of each other nothing special will happen. As they have the same sprit the one above will cover all the others that are below and it will only be possible to see the last pit demon to be stacked. For example:
you start putting all the pit demons in a skm: 1st black, 2nd blue, 3rd red, 4th brown and last green. In this result, all the others except the green were hidden.