To refill your Drive Gauge, simply walk into a save portal with Sora still in a Form (any Form). Head to the World Map and go to wherever you need to, even the same planet you were on. When you go back in, you should have your Dirve Gauge maxed out.
How do you beat Kingdom Hearts 2?
Marluxia is found near the savepoint in Beast’s Room. He casts doom right at the beginning of the battle, where you can be hit a number of times equal to your current level, and then you will automatically die.