From Sonic Retro

Yago (ヤゴ) is a badnik in Sonic the Hedgehog CD's Tidal Tempest. It isn't listed in any instruction manual, however it is referred to as "yago" (the Japanese word for dragonfly larva) in the game's source code. It is a badnik that swims close to the underwater ground. When you approach from up front, it starts swimming faster in an attempt to hit you before you can escape. But you can always jump and hit it instead.

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