Purply's Crown is an item that can be found in Momodora I.
The item itself is just a collectable, it has no in-game effect.
Just like the Shell Fruit, Purply's Crown is hidden inside solid matter. To obtain Purply's Crown, you have to go to the fourth room of Area 5, just after the room which looks like a long, upward-going pipe with turbines on the sides. Just at the bottom of the room, go into the left corner: you will fall through the floor and onto the crown.