Use WASD to move. Click to throw a Pikmin. (You'll need to be touching it and have it chosen as the colour you throw) Space to call for your Pikmin. (They need to be touching the purple circle) Use 1, 2, and 3 to change the colour of the Pikmin you throw. Only blue Pikmin can go in water. The pellet posies give you more Pikmin if more Pikmin are touching it.
