The one-on-one duels are a tough ordeal, but there is a way to make it a lot easier. Just keep casting protective and curative magic (GUARD BEAST is a must!!) for 15 turns. The sub-boss will disappear and you will emerge victorious.
Play as Ventarbre
Although it is generally believed that Ventarbre is a non-playable character, there is a way to play as him. Right after the Johan the Assasin scenario, choose to go to Weissland or Laubholz... Your party will consist of Gustave, Johan, and Ventarbre! With this party you can try to defeat the Megalith Beast or tackle the Ghoul Tower.
Mega T260/T260G
Equip T260/T260G with 3 Hyper Blasters and 4 War-lord Armors in its Type 1 body. It will have 999 HP and 99 defense.
Play as Rouge
At the begining of the game select Lute. After you arive at Manhatan go to Luminous and first get the magician Rouge, to join you. Now you can play as Rouge, but if you travel to Magic Kingdom you will lose him.
Obtaining Suzaku
While in Mosperiburg in search for the Shield Card, you can get Suzaku as a playable playable charactor. Defeat the fairie on the first screen, yhen go to the area with three boars in it. You'll see a snowman on the southern edge of the clearing, which takes you to a fight with Jotnar. The Jotnar is really tough. It helps to have Ice Crystals, Gendu Sheilds, and Pearl Hearts to help nulifie its ice and water attacks. Once Jotnar is defeated, return to the previous cave and take the right branch to find a defrosted Suzaku Jr., who joins your party.
Dream Super Combo
This attack is acquired by specializing in Fighting skills. Liza is the best as she can get this developed the quickest, but others will work… just be prepared for a long wait (Fei-on took me 23 hours of work to get all the skills)
Sliding
Suplex
Babel Crumble
Giant Swing
Equip all four on a single character and the DSC option will appear in your attack menu. Warning! This takes 18 WP, so save it for bosses or if you're just experience building.
Easy Money
Money can be pretty hard to come by, but there is a way to gain access to an infinite amount of funds:
Simply go to the Junk Shop in Scrap (located in the lower right hand corner) and pay the shopkeeper for your choice of items (you can pick 7.) After taking your items from the barrels and boxes, go and talk to the shopkeeper again. Tell him you'd like to sell, and point to the last item on the list, the Hyperion Bazooka. Press the accept button several times, regardless of whether or not you actually have one.
Then, go back to the room where you picked your items: You can now pick 7 more! This can be repeated as often as you like. To get infinite money, head to the barrel in the middle left and keep searching. Pretty frequently, you should find Hard Leather, which can be sold in Koorong for 45 credits each. Repeat until you have about 50 or so Hard Leathers, and you can make a fortune!
You can also use this to find some average-strength equipment (simply look all around the room) with little effort. You will have to pay every time you leave and come back to get more, however (it's about 600 credits, I think.)
Note: After a while, the goods offered in the Junk Shop will increase in value, and Hard Leather will no longer be offered. When this happens, for the Infinite Money, simply go to the upper left-hand box and get the various swords there. EACH of these swords can be sold in Nakajima Robotics, in Shrike, for even more money than the Hard Leather!
Getting HP
Your Hp increases after every battle, depending on your maximum HP. Defeat enemies weaker than you to restore your HP for a big battle. It is best to be in a duel battle and use No Moment which is unavoidable and costs 1 WP. The combo to use No Moment is Ready-Ready-Ready-Slash. To make it easier to use the move, make sure your character is fast.