What are ghoul coins used for?

I’ve been getting a ton of ghoul coins and I don’t know what to do with them
What are the point of these?

They are used as currency in the Ghoulcery store, which sells Halloween items. You had to find Lil Pup in the maze during the event in order to access the shop. Now that the event is over, it’s in Celebrations, so if you still have those ghoul coin you should still be able to spend 'em there.