Final Fantasy VI/Espers

Ramuh, Kirin, Siren, and Cait Sith
These Magicite are given to you by Ramuh in Zozo. These are impossible to miss, given that you have to talk to Ramuh to move the plot along.

Ifrit and Shiva
They can both be found at bottom of a pit in the Magitek Research Facility. To advance the plot, you must fight and defeat them. Once beaten, they yield their Magicite to you. You only need to pick up Shiva to continue with the game, but picking up Ifrit is highly advised.

Unicorn, Maduin, Catoblepas, Phantom, Carbuncle, and Bismarck
Shortly before leaving the Magitek Factory, all of these Espers give their Magicite to you. You can't avoid taking them.

Golem and Zona Seeker
These can both be found in the Auction house in Jidoor. You just need to buy them in the auction for 50,000 Gil each. If missed, they can be bought in the World of Ruin.

Seraph
This Magicite can be bought from a traveling salesman in Tzen for 3000 Gil in the World of Balance or 10 Gil in the World of Ruin. You learn of this man in either world from one of the old men near the dock area. The man is walking/hiding behind some trees in the upper-right corner of the town, all the way in the back.

Quetzalli
After getting the airship in the World of Ruin, return to Cid's Island, and you will find this Magicite on the beach.

Fenrir
After defeating Humbaba in Mobliz for the first time, a kid will give this to you if you talk to him.

Valigarmanda
Go to Narshe and go back to where you found it before. If you manage to defeat it, the Magicite is yours. Afterwards, a cave opens up to reveal the Yeti's Cave.

Midgardsormr
This can be found in Umaro's Cave in Narshe, simply search the skull there, defeat Umaro, and it's yours.

Lakshmi
Defeat Chadarnook in Owzer's house in Jidoor, and collect it from Owzer's bookshelf.

Alexander
Go to Doma in the World of Ruin and do the entire Cyan quest. At the end of the quest, it will be sitting on the throne in the throne room of Doma Castle.

Phoenix
Go to the star shaped mountain range north of Tzen and land in the middle. Complete the Phoenix Cave, and Locke will give you this Magicite.

Bahamut
Find and defeat Deathgaze while flying around in the airship. Defeat it, and Bahamut is yours. Be sure not to use the Vanish/X-Zone trick, or the game will not count Deathgaze as defeated and it will still fly around. However, Vanish/Doom will work every time. However, the vanish/death trick doesn't work in the GBA version, so you have to fight Deathgaze normally. Deathgaze does not recover its HP, so it can be challenged as many times as you want until it is defeated.

Crusader
Defeat all 8 dragons, and this Magicite will suddenly be given to you.

Odin and Raiden
Go to Figaro Castle, in the World of Ruin, and try to move the castle somewhere else. It will get stuck under the sand, and you can enter a new cave via a hole in the prison level. Go through the cave and enter the Ancient Castle there. Walk straight ahead and talk to the statue of Odin. It will yield the Odin Magicite. To get Raiden, stand on the right throne, walk five steps down and press the A button. A secret passageway will open. Go down it, and you will find a statue of a girl. Talk to it, and the Odin Magicite will become the Raiden Magicite.

Once you transform Odin, its Meteor spell is lost.; fortunately, that spell can also be learned from Crusader and Celes learns it at Level 99, so don't worry about it.


 * Note: Odin is the only esper in the game who can boost your speed attribute, except for the GBA-exclusive Cactuar.

Ragnarok
In the World of Ruin, go to the Narshe Weapon Shop with Locke, and he will unlock the door. Inside, a man will ask you if you would rather have the sword Ragnarok or the Magicite Ragnarok. Choose the Magicite, and it will be yours.
 * Note: Ragnarok is the only Esper in the game that can teach a character Ultima, but if you want the sword it is also possible to teach Ultima by equipping a character with the Paladin Shield. Terra also learns it at Level 99.

Leviathan
Leviathan is only in the GBA version of the game. In the World of Ruin, talk to the man near the entrance of South Figaro. He tells you about a creature he saw in the ocean. Afterward, go to Nikeah and ride the ferry. During the trip, Leviathan will attack. Defeat him to gain his magicite.
 * Note: If you didn't get Mog's Water Harmony in the World of Balance, this battle also offers one last chance to obtain it.

Gilgamesh
Gilgamesh is only in the GBA version of the game. In the World of Ruin, buy Excalipoor in the Jidoor Auction House for 500,000 Gil. Then bet it in the Dragon's Neck Colosseum. One of your characters will have to fight an Onion Dasher. After the match, Gilgamesh shows up and challenges your party for Excalipoor. Defeat him, and you get his magicite and a Merit Award.

Cactuar
Cactuar is only in the GBA version of the game. In the World of Ruin, defeat ten Cactuars in the desert near Maranda. Eventually, you'll be attacked by a Gigantuar. Defeat him to get the Cactuar magicite.

Diabolos
Diabolos is only in the GBA version of the game. Defeat Kaiser Dragon in the Dragon's Den for it.