Hotaru

The Firefly is an enemy found in the Game Boy Advance game Wario Land 4. It only appears in the boss battle against Cractus in the Emerald Passage. Each time Wario damages Cractus, it will stand immobile on the stage for a few seconds. While it does so, it drools a clear, toxic liquid which will transform Wario into Zombie Wario, which is a completely useless transformation in this situation and it would just waste valuable time. As soon as he transforms, a Firefly will be seen, slowly moving across the screen. Since light can reverse the effects of Zombie Wario, the player would need to try and touch the Firefly by jumping. But as slow moving and jump-deficient Zombie Wario can be, this may waste a fair amount of time. As soon as the status effect is reversed, the Firefly will disappear. It will return again whenever Wario transforms again.

In the beta version of Wario Land 4, the Firefly had a very different appearance to the final version of the game. It has much less of a glow that surrounds the creature, and it could be seen from the very beginning of the battle, rather than only when Wario has trandformed.