TM18 is a TM containing the move Rain Dance. Rain Dance is a Water-type move that causes rain for five turns. Many water type trainers who are going to be fighting for a long time will use this move. The rain increases the damage of Water-type moves by 50%, while reducing the power of Fire-type moves and SolarBeam by 50%. It also raises the accuracy of Thunder and Hurricane to 100%, and decreases the healing potential of Synthesis, Morning Sun, and Moonlight to 25% of the user's maximum HP.