I write fantasy books, so I often come up with magic systems. This one is one of my favourites; people who are born on a full moon have a chance to be blessed with the moon goddess's powers. These people can carve Runes into wood or other materials. There are two Runes, a Water Rune and a Wind Rune. The Runes have to be drawn precisely, no mistakes, to work. The Water Rune pushes water away from it, and the Wind Rune pulls air/wind toward it. The Wind Rune is commonly sketched on the sail of a ship to speed it up. The Water Rune is often used for bombs--opening a barrel full of water and putting a cube with a water rune sketched on all six sides, and then closing the lid will cause the barrel to explode because the water has nowhere to go.