Final Fantasy VI/Espers

List of Espers, Their Summon Effects, Level Bonuses, Spells, and Locations
&sup1; Odin becomes Raiden

Ramuh, Kirin, Siren, and Stray
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 Magitech Factory. 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.

Unicorn, Maduin, Shoat, Phantom, Carbunkl, and Bismark
Shortly before leaving the Magitech Factory, all of these Espers give their Magicite to you. You can't really avoid taking them.

Golem and ZoneSeek
These can both be found in the Auction house in Jidoor. You just need to buy them.

Sraphim
This Magicite can be bought from a traveling salesman in Tzen for 3000 GP in the World of Balance or 10 GP in the World of Ruin. You learn of this man in either the WoB, or the WoR 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.

Palidor
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 Phunbaba in Mobliz for the first time, a kid will give this to you if you talk to him.

Tritoch
Go to Narche and go back to where you defended him before. If you manage to defeat him, the Magicite is yours.

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

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

Alexandr
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.

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

Bahamut
Find Doom Gaze while flying around in the airship. Defeat him, and Bahamut is yours. Be sure not to use the Vanish/X-Zone trick, or you will not receive Bahamut. However, Vanish/Doom will work every time.

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 the 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, it is lost, so learn any spells you want from it before "upgrading" it.
 * Note Odin is the only esper in the game who can boost your speed stat.*

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 that 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.