Since we're in the Magic Kingdom and also in Square-land, there has to be magic. Getting magic usually happens pretty automatically, but you might miss it anyways, so here is a nice little list to get all the spells. "Oh that Magic Kingdom in the sky!"

We'll go in order of acquisition.

Fire: consumes 1/2 MP.
Effects: Basic fireball spell, it will shoot a little shot of fire directly in front. If you lock on to an enemy, it will shoot towards that enemy within a certain range.
Acquire: Donald gives to you in Traverse Town upon your first meeting.

Fira: consumes 1/2 MP.
Effects: You'll get a bigger ball of fire.
Acquire: After you beat Genie Jafar in Agrabah.

Firaga: consumes 1/2 MP.
Effects: The biggest fireball of them all! Make Lina Inverse jealous.
Acquire: The princesses will upgrade your magic to Firaga after you defeat the Behemoth inside Hollow Bastion the second time you go there.

Blizzard: cosumes 1 MP.
Effects: You get 7 little shots of ice shooting at your enemies. A nice wave effect to hit groups.
Acquire: The Cheshire Cat will give this to you if you find all 4 pieces of evidence.

Blizzara: consumes 1 MP.
Effects: You'll get 7 bigger bits of ice.
Acquire: You get this after you beat Jafar the first time in Agrabah.

Blizzarga: consumes 1 MP.
Effects: HUGE chunks of ice smash into the enemies.
Acquire: Defeat the Behemoth in Hades Cup and you can get the final upgrade.

Thunder: consumes 1 MP.
Effects: Thunder bolts will hit the area that surrounds you or, if you lock onto something, the area that surrounds the object you locked onto.
Acquire: Phil will give this to you before you start the barral trials in the Coliseum.

Thundara: consumes 1 MP.
Effects: You get larger bolts of lightening and the range is a little bigger.
Acquire: Beat the HUGE Ursela, and you'll gain this upgrade.

Thundaga: consumes 1 MP.
Effect: HUGE thunderbolts, like Zeus! The range is bigger too.
Acquire: Defeat Cerberus in Hades Cup.

Cure: consumes 1 MP.
Effect: You can replenish a little bit of HP for one character.
Acquire: You gain this all important spell in Deep Jungle, after you beat Clayton and the Stealth Sneak.

Cura: consumes 1 MP.
Effect: Replenish more HP!
Acquire: This is automatically upgraded in Neverland, right before you jump off the ship and learn to fly. "Just believe, Sora."

Curaga: consumes 1 MP.
Effect: Replenish a LOT of HP.
Acquire: You can get this after the Square gang goes back to Hollow Bastion. Talk to Aerith a couple of times and she'll grant you this power. Nifty.

Aero: consumes 2 MP.
Effect: A protect spell, reduces enemy damage.
Acquire: You gain this defense spell after you beat the Opposite Armor the second time you go to Traverse Town.

Aerora: consumes 2 MP.
Effect: Not only does it reduce and sometimes deflects enemy damage, it can also damage enemies who touch it.
Acquire: You can find this spell in the room locked by the Yellow Trinity in Neverland.

Aeroga: consumes 2 MP.
Effect: This spell will deflect most attacks and also damages those enemies that touch it.
Acquire: You can get this upgrade if you find all 99 of the Dalamation puppies.

Stop: consumes 2 MP.
Effect: This will freeze a trageted enemy. While it's frozen, you can hit it and accumulate damage that it will take after it un-freezes itself.
Acquire: You can get this spell after you beat the Parasite Cage II, the one in the stomach up the throat.

Stopra: consumes 2 MP.
Effect: This is like Stop, except that it can hit an area and not just one enemy.
Acquire: Get this upgrade by finding Eeyore's tail in the 100 Acre Woods.

Stopga: consumes 2 MP.
Effect: Like Stopra, except that its range is much larger and can affect more enemies.
Acquire: If you can defeat the Phantom in Neverland, you can gain this spell.

Gravity: consumes 1 MP.
Effect: This spell is a ball that crushes the target into the ground. The damage that the enemy takes is based on a percentage, so you can't kill with it directly.
Acquire: You can either get this spell by winning the Phil cup, or you can getit by beating Oogie's Manor in Halloween Town.

Gravira: consumes 1 MP.
Effect: The percentage you take off the target is bigger and also the range gets wider.
Acquire: If you got the spell in the Phil Cup, you'll get an upgrade in Oogie's Manor. If you got it in Oogie's Manor, you'll get this upgrade when you beat the Phil Cup.

Gravirga: consumes 1 MP.
Effect: Has the highest percentage of damage and also the largest range.
Acquire: You can get this if you defeat Hades in the Hades cup.