Don't use these tips if you are still enjoying the game, and you don't want help yet! These are things to make the game easier when you are having trouble.
Grimoire with more slots Edit
When Synthesizing Grimoire stones, there is a way to increase the number of slots in a Grimoire stone without using a Grimoire Stone with more slots. Find a Grimoire stone with more slots and press, A then B, then up or down, then press A to select a new Grimoire stone with less slots. This needs to be done very quickly, and if it works the skill slots in the top right corner should now say the number of the stone with more slots. Then use the stone that says the wrong number of slots to synthesize, and it will end up with the number of slots of the Grimoire stone that had more slots originally.
Duplicating items in battle Edit
When you have a character that has boost, you make them use an item, then press B, press boost and the item is duplicated. It is possible to duplicate an item many times in one turn. However, make sure that the character that uses the boost to duplicate isn't the last character to select attacking/defending/etc last because other wise they will USE the item. If you have trouble getting all the monster drops or getting lvl's, you could duplicate Formaldehyde or Divine Gift. It is also very useful to duplicate Nectar II in battle when you are going to run out. This only duplicates things that are consumables that can be used in battle. This glitch doesn't work in the European Version.