Mothula is a giant moth that flies around the arena, dropping poisonous dust and occasionally charging at Link. The arena floor also has conveyor belts that can push you into spikes. The key to defeating Mothula is to use your Feather (or Roc's Cape) to jump over its dust attacks and avoid the spikes. Continuously attack Mothula with your Wooden Sword whenever it's within reach. It will occasionally become temporarily invulnerable after taking damage, so just keep dodging and attacking. The conveyor belts can be tricky, so try to position yourself strategically to avoid being pushed into danger. Reward: Heart Container and Bright Sun (Essence of Nature).
