How do you beat the boss in never land in kingdom hearts day 301

You have to keep hitting the tail bits and after one falls off just dodge all of the attacks. Once you knock off the last one it will go crazy. After the coins stop shooting out of his mouth go up to him and hit the gem (i believe under his neck.). Keep doing this until he dies. Note: Make sure to bring a lot of Potions and higher grade potions. Fire, and Ice spells don't really work. If you can pin point where the monster will be Thunder spells will work.
Hope this helps and good luck!
----Tamaki242