On Windfall Island is a man named Doc Bandam, who runs a potion shop. In order to provide the opportunity for you to buy more potions, he needs Chu Jellies in order to make them. One such potion is the Blue Potion, which requires you to hunt down Blue ChuChus. These are special and hidden ChuChus, of which there are only 23 in the entire game.
Defeating them will yield a Blue Chu Jelly, which you can bring back to Bandam when you have 15. Note that you can also steal them from the Blue ChuChus with the Grappling Hook. They only drop the Jelly once, so you cannot keep going back to the same one to get more. On subsequent steals/kills, they drop a Yellow Rupee, which is worth 10. Remember that they must be stunned first before killed, as they have electricity flowing through them.
LOCATIONS
#1) Star Island - You will need either the Bombs or Power Bracelet to get this Blue ChuChu. It is hidden under a huge rock on the island, so use either of the two items above to get rid of the boulder.
#2) Northern Fairy Island - You'll find this Blue ChuChu by the palm tree on the eastern side of the island.
#3) Crescent Moon Island - There are two Blue ChuChus on this island, with both of them being near the treasure chest.
#4) Crescent Moon Island - There are two Blue ChuChus on this island, with both of them being near the treasure chest.
#5) Overlook Island - On the top of the island, you can use the Hookshot to get across to the other side of the island. Once you do, you will find the Blue ChuChu there.
#6) Mother and Child Isles - This Blue ChuChu is located on Child Isle, the smaller of the two.
#7) Spectacle Isle - You'll find this Blue ChuChu underneath the short wooden bridge by the sand.
#8) Pawprint Isle - The Blue ChuChu will spawn on top of one of the rocks on the main island.
#9) Western Fairy Island - The Blue ChuChu is located near one of the palm trees on the island.
#10) Rock Spire Isle - Climb up the slope on the one end and make your way across the island, blowing up the boulders with Bombs that are in the way. When you make it to the other side, you'll find the Blue ChuChu there.
#11) Tingle Island - This one spawns near the wooden sign on the island.
#12) Eastern Fairy Island - This one spawns near one of the palm trees on the island.
#13) Thorned Fairy Island - The Blue ChuChu spawns near one of the palm trees on the island.
#14) Needle Rock Isle - The Blue ChuChu is located on the ring island, so keep going around until it decides to spawn.
#15) Stone Watcher Island - This one is located at the top of the island, behind the giant face statue.
#16) Bird's Peak Rock - Above the door on this island is a wooden peg you can use your Grappling Hook. Instead of swinging, stop and then climb the rope to stand on top of the wooden peg. From here, you can get on top of the island to find this Blue ChuChu.
#17) Diamond Steppe Island - You will need the Hookshot for this, as you need to use it on a tree to get onto the island. The Blue ChuChu is located on the third level of the island.
#18) Shark Island - There are four switches on this island, which need to be used with the Iron Boots, sword, Skull Hammer and one stepped on. Do this fast enough and an updraft appears near the island. Go to the opposite end and stand on the ledge jutting out. Change the wind direction to blow southeast and then glide to the updraft, which will allow you to get to the top of the island, where you'll find the Blue ChuChu.
#19) Southern Fairy Island - The Blue ChuChu spawns near one of the palm trees on the island.
#20) Cliff Plateau Isles - The Blue ChuChu is on the largest island of the whole group. To get there, you need to find the hole in the ground on the fourth little island. Make your way through this cave and you'll reappear on top of the big island.
#21) Horseshoe Island - You'll only find this one at night. On this island, you need to use your Deku Leaf to blow the nuts into the holes so that spiked vines will go into the ground. The Blue ChuChu is located to the right of the second hole.
#22) Angular Isles - The Blue ChuChu is on the top of the main island, next to a treasure chest. To climb to the top, you will need to pull out some blocks with writing on them.
#23) Boating Course - Get on the one island that you can and you'll need to set the wind to blow north. From the highest point of the first island, use your Deku Leaf to glide to the other island. The Blue ChuChu is on the grey-colored ground.
