Please elaborate on what you meant by "How to defeat boss battle" because
Because your question is unclear, if you are unable to improve upon it, it will be deleted in 24 hours. Perhaps it will be clearer if you tell which game it comes from, or move it into the form of a question?
I don't really know what you're talking about, but generally when you fight a boss in the Kingdom Hearts series, you want to make sure you are leveled up. If you haven't been fighting the Heartless/Nobodies/Unversed/Dream Eaters that tend to appear in groups as you walk around in the world, you likely do not have as much exp. as would be ideal for fighting whatever boss it is you're fighting. My advice is, whenever you see a group of enemies appear, take the time to get rid of them all so you can level up. It makes boss fights a lot easier. Also, make sure you have good commands in your command deck. Make sure you have a good balance of healing commands and attack commands, so you don't have to scroll to far in your command deck if you need to heal quickly. It is always heplful to have leaf bracer and once more installed, as well, as leaf bracer will ensure that you never take damage when healing, and once more ensures that if you get caught in an intense combo that you cannot get out of, you still have a tiny bit of HP left, even if the combo should have killed you. Since I don't know what game you're referring to, or which boss you're fighting, that's about all the tips I can give you. If you specify the game and the boss, we can probably provide a more accurate answer. — DarmaniTheFourth ~Talk~ 22:29, June 28, 2013 (UTC)