Instructions
Travel around the Great Sea fighting Bokoblins. These creatures carry joy pendants, which you can gather when they die, or steal with your grappling hook.
Fight the Bokoblins until you obtain 20 joy pendants.
Take the joy pendants to Mrs. Marie on Windfall Island. This island is on the upper left corner of the Great Sea.
Give Mrs. Marie the pendants. In exchange, she will give you the Cabana Deed.