Bumble Buster

Bumble Buster is a mini-game that is in Twilight Town in Kingdom Hearts II. Both Roxas and Sora can play it, though only the former gets munny. It involves killing honey bees in the Tram area in Twilight Town. Completing it faster reaps you more munny (only when playing as Roxas).

While playing as Sora, it's required to beat in a certain amount of time in order to complete the journal.

Sora's reward
To unlock the secret ending, you need to complete Jiminy's Journal. Part of finishing Twilight Town's journal entry involves playing this mini-game. The Jiminy Objective is to complete with 10 seconds.

Strategy
The goal is to clear out the local bees. Press to lock onto the bees, but release the lock-on feature before swinging. This way, the yellow auto-target will zero in on whichever swarm is closest.

Advanced tactics
The key to defeating all of the bees within the set time is bringing them together with the Magnet spell. The more powerful the spell, the more likely any bees at a distance will be drawn in. Follow this up with a combo or jump in amongst them with a Fire or Thunder spell.