Toadofsky sidequest
The Toadofsky sidequest allows you to get a membership card for the juice bar in Tadpole Pond, allowing you to purchase more items at a cheaper price.
Read the sign on Frogfucius' island to see "So La Mi Re Do Re Do Re"; when you jump back across the tadpoles, run to the southeast and take the pathway into Melody Bay. This area is a small mini-game like area where you can receive the Alto Card from Toadofsky (the composer on the northeast side of this area). He can also give you some information about the mini-game, but to get it done, simply go back to the southwest side and step on the stone there.
- Making music
To compose music, you will place the tadpoles in a sequence which will then be replayed after you set them all up. If you place them in the correct positions, you'll receive the Alto Card (an item that lets you into an area much later in the game). When you step on the stone on the southwest side of the pond, a tadpole will appear and begin swimming along the width of the staff. When the tadpole has landed on the place where you want it to stay, press 
to jump on it. You should do this just when the tadpole begins moving towards the place where you want it to stop, otherwise you might end up jumping on the location just after the one you wanted. To receive the Alto Card, place tadpoles on the following locations: second to bottom line (So), space just above the second to bottom line (La), top space (Mi), second to top line (Re), second to top space (Do), then Re, Do, and Re once more. If done correctly, Toadofsky will be extremely pleased and will rush off after giving you the reward.
Culex sidequest
Using the "Shiny Stone" on the sealed door in Monstro Town reveals a hidden boss named Culex. Contrary to popular belief, the Culex character is not from any particular Final Fantasy game and instead simply represents a sort of generic "Final Fantasy-ish" boss.
The Earth, Wind, Fire, and Water Crystals that accompany him originally appeared in both Final Fantasy IV and Final Fantasy V. During the fight with Culex, the Final Fantasy IV boss music plays in the background. When Culex is killed, the original Final Fantasy "victory fanfare" plays, and the Final Fantasy "introduction" music plays during Culex's conversation in the overworld.
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Culex with Earth, Wind, Fire, and Water Crystals.
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Close up of Culex.
