My son is turning 4 in a few weeks and we are giving him a “knight” birthday at his request. I want to make his cake but a)it’ll just be me, his dad, and him eating it and b) everything knight related looks so complex! He loves The Sword in the Stone so I’m thinking of doing something like this

I found the same plastic sword available at Party City so I’m set there (it’s 15” long for reference). How much cake would you say that is? What’s the easiest way to shape it like a rock? (He’s also saying he wants it flat like in the Disney movie so I could go that route instead if it’s easier) How much fondant do I need?

Thanks for any advice you can give me!