A few people asked for help with some bosses that they found were hard. Here is a general list of ways to do better on those tough guys :) :
1) Full Energy One thing that really helps in fighting the boss with full energy. If you're only missing a little mp or hp, then it may not be too important to do this, but if say your hp is down to 10 and you're fighting a boss, don't expect to win.
2) Stock Up It is helpful to have one or two potions or ethers on you, just in case you get in a tight spot and need it. Ethers are especially helpful for Serena.
3) Serena's Cure Spell Serena's cure spell can cure hp for ALL members of your party for the same price as one. This is a very helpful bit of information to know. Once you get more than one person in your party, it is a good idea to have Serena cure everyone and have the rest of the party just attack, this will save time. If only Serena is hurting (or maybe just 1 person), then it would probably be better to use someone else's cure spell on her, so you save Serena's mp.
4) Level Up If none of these tips helped you beat that boss, try leveling up some more. The problem may just be that you're not strong enough yet to take the boss on. Try gaining a level or two.
This game will no longer be updated. This is the final version (made by me at least).