Fastest way to level up in Kingdom Hearts 358 2 days?

A good way to level up both you and your forms (valor, wisdom, master, and final) follows.

Valor, Wisdom, Master - Go to Hollow Bastion Merlin's House. Turn into your desired form leave and defeat the heartless. DO NOT LET YOUR DRIVE GAUGE DROP TO 0. Before the gauge drops to 0 go back to Merlin's House and go to the world map. Just repeat that process.

Final - Use the same process as above but go to The World That Never Was