Tips for Kingdom Hearts II - Day two

Find... Lightning gem
Find it Visit Space Paranoids or Hollow Bastion later in the game to find one of these. The monsters who hold them are usually Surveillance Robots and the hard-as-nails Armored Knights.

Find... Lucid gem
Find it Go to Hollow Bastion or Space Paranoids and kill either a Bookmaster or a Magnum Loader to make them drop one of these, which is a key ingredient in the Soldier Earring we mentioned earlier

Find... Mythril gem
Find it Like the mythril crystal, you can only get this from random treasure chests, or by synthesizing one yourself. You can use it in free development to make a Mage Earring for Donald.