After the opening scene head up to King’s Den and speak with Simba. You learn the "Running Tackle" maneuver now, so head to the Stone Hollow and speak with Rafiki. Swing over to the Elephant Graveyard where Shenzi, Banzai, and Ed are located. You just have to chase them down and use Running Tackle, then combo them. You can also catch them as they leap. Simba’s Limit is great for catching the hyenas.
BONUS : Accessory Slot (Sora), HP +4 (Donald), MP Rage (Goofy), HP +5 (Simba)
Head to the Oasis after going to Pride Rock; Timon points this out. After a scene at the Oasis you’ll be taken back to Pride Rock. Save your game and put on some Thunder Resistant equipment and take off any "Auto" ability for the ensuing boss fight.
BOSS - Groundshaker
This Heartless may be huge but it’s one of the deceptive ones. Use "Leap" to dodge the attacks then "Fend" to knock out the big guy. Attack his eyes during this time or launch up to the top of the Groundshaker. From here you attack the shaman-like enemy at the top. Lay into this thing until it gets vicious and forces you off.
Alternate between the eyes and the shaman to get the most effective attack then use Wildcat so you can finish off the battle. Towards the end try to get underneath the Groundshaker and use "Fend" to stun the beast.
Rewards : HP +5 (Sora), Thunder Element (Sora), HP +5 (Simba)
With that, this world is complete. You have Thundaga now so you can visit Sebastian if you like.