7. You can gain a level every two minutes
A great way to level up in general is to head to one of the areas where the enemies respawn every time you enter. The garden in Mickey's Castle is a good spot to camp early in the game, for example. There's at least one solid location in The Land of Dragons too.
But the Mother Lode for leveling up appears later in the game. After your second trip to the Pride Lands, you can head to Pride Rock with a Magic level of at least 53 and farm the enemies called Rapid Thrusters. They'll appear in swarms. Turn off all of Goofy and Donald's healing abilities, and take damage yourself until that annoying "low health" siren starts. If you have them, equip the Experience Boost ability and swing the Gullwing keyblade. Then, use Magnega and Thundaga to wipe out all of the monsters flying about - the swarm will reappear every time you leave the area and return. Instant kills and the resultant fountains of experience points make it possible to gain a level every 90 to 180 seconds.
Above: No, no, no! We like beating these things. Not being them.
8. You can be heartless ... yet live on
When you use the Drive Gauge to literally merge with Donald or Goofy in Kingdom Hearts II, Sora transforms into one of five Drive Forms. The first three - Valor, Wisdom and Master - are obtained simply by playing through the story, but the fourth and fifth are somewhat harder to come by.
Final Form is the best and the most useful, but only shows up after you've used the first three forms frequently. The fifth form is commonly referred to as Anti-Form, which transforms Sora into a dark creature with yellow eyes and long tendrils - more or less the Heartless side of our hero. While we realize this sounds unbelievably cool, it honestly grows tiresome, as the Anti-Form is weak and limiting. The bad news - it’s random, and gets more likely the more you use Drive Forms. The good news - using Final Form as often as possible appears to lessen Anti-Form’s chances of bothering you.
By the way, there's a trick to refilling your Drive Gauge. Once you've triggered it, if you find a save point and enter the world map before the Drive Gauge is completely empty, using the map to "re-land" in your current location, your drive gauge will be refilled. Or, you can just enter a tournament in the Underdrome, once that's unlocked. This will fill you up, and you can just quit out of the tourney and carry on.