Not the best toy for creating mario stuff but here's what I did with only a 300pc set. FYI you run outa colours fast so I had to spread things out.
It shows on the box you can do some 3d stuff with it but I found that rather challenging to make something and have it structurally solid.
Step 1: Mario Flower
Multicoloured flower, not enough pcs to do a solid border
Step 2: Hello Kitty
Hello kitty with ribbon
Step 3: Heart
What I created with the leftover pieces just for fun