Misc. TIPS
Save the Refugees

Outside Railhead, when you get to the Switching Point, some Refugees are trying to get on board the train while avoiding elimination by the Border Guards.  You are controlling the Refugees, and you have to move them away from the guards since all they can do is move and use healing items, they can't attack.  Each refugee saved is worth 10 XP to every member of the party, so try to save as much as you can. 
HOW TO DO IT ?
You have to get Dantares across the tracks to the switching post by his 3rd turn, activate the switch and defend the refugees. While you're moving Dantares, also move the refugees away from the guards, along the fence, until they can cross the tracks.  Once crossed, head towards Dantares.  Save before the battle and use a different save file when making critical decisions.  It helps if you have a memory card.

LAST MINUTE NEWS :

All you get from saving ALL refugees is 10 XP per refugee saved for each member. Also, if you have Scenarios 2 and 3, the father/elder of the group gives Julian a Justice Sword as thanks for his role in their survival (thanks to NightBird from the Forum on this one...).
Longer lifespan for re-usable items !

In the game, you will find many items which can be used many times, such as Black Ring (Blaze LV2), Swift Boots (Support LV1), Ibiru Ring (Spark LV2), Magic Ring (recover MP), Ark Halberd (Spark LV3) and others.  After being used a few times, they crack and can't be used until you get them repaired. But I have found that the items break randomly.  They can break after 2 or 10 uses, you can't predict when it will happen. 
Solution: If you can afford to, save the game just before you plan on using such an item (during battle).  If the item cracks after use, simply reset the game and start over.  The item may not crack that time.  Repeat until item doesn't crack, and you can use the same item during the whole game without repairing it once !
Don't kill Spiriel !

In the Catacombs, you will face both Basanda and Spiriel (under the control of Bulzome).
Killing Spiriel is USELESS, but she can be quite dangerous, so you should put her to sleep and move on to fight Basanda.  So have 1 or 2 characters (Grace/Masqurin/Noon) equipped with weapons that give you Sleep Magic, and put Spiriel to sleep as soon as possible.  I suggest saving the game before casting the spell, so if the spell doesn't work you can reset the game until the spell works.  When you defeat Basanda, Spiriel will be free from Bulzome control and be grateful.  She will say she doesn't want to help the Empire anymore knowing that they sided with Bulzome, but that she cannot help the Republic either, and she doesn't know what to do.  What's the use ?  SHE JOINS JULIAN in Scenario 3, that's why !!!
After the battle with Basanda, and after Fynnding joins the party, you will return to Malorie to talk to Tristus and Margaret.  When you're done talking to them, visit the Weapons Shop, which will be open for business.  There are 2 things to do there:

Harrass the shopkeepers !

Simply put, you should "harrass" the shopkeepers...
That means pressing "C" button to start the conversation, then pressing "B" button to cancel that conversation.  After a couple of times, the shopkeeper will "remember" that he has a new arrival of weapons/items that could be of interest to you.
Those weapons/items will be sold under Deals if you don't buy them immediately.  That trick works in every shop, in every city, so try it !


Visit the Items Shop Keeper

From inside the Weapons Shop, cross over to the Items Shop by going through the door in the wall that separates the shops.  When you talk to the Keeper, she will GIVE you a Healing Rain (restores Full HP to every member of the Force - same as Aura LV4) to thank you for saving the city.  Use it well, there are only 2 Healing Rains in the game, and one is found in one of the Ruins.
Fighting the Skull Mage in the Holy Place

After defeating Basanda, and Fynnding joins, you SHOULD return to Malorie, both to talk to Tristus and Margaret and to revive fallen members.  You can also re-organize your party for the upcoming battles. Have both Eldar and Fynnding in your party, you'll see why...

Then, head back for the Catacombs, but don't go fight the Colossus and Arrawnt yet.  Instead, head for the other door, where there is a sign to warn you of danger, and enter.  Inside, there will be 4 levels, each more dangerous than the previous.  There, you should also find more Mithril.

The idea is to defeat each level's BOSS to gain access to the next level.

Level 1: Succubus (BOSS)
Level 2: Harpy (BOSS)
Level 3: GigaBreaker (BOSS)
Level 4: Skull Mage (BOSS)

With Eldar and Fynnding, Succubus and Harpy will be easy to defeat because they can fly and reach the boss quickly.

GigaBreaker is VERY sensitive about Spark LV4...

Skull Mage has 1000 HP, but only when he has less than 600 HP left will you know the exact count, so I suggest you note every hit to keep track of your progress.  Skull Mage uses primarily Tiamat LV2, to summon a big blue Dragon which hits at range: 1 around the target.  Total damage around 80 HP, distributed among the targets (the more characters hit, the less damage to each).  He also uses Soul Steal LV2 (same range), which can deprive you of either 10-15 HP or YOUR LIFE !  The reward for defeating Skull Mage: the Tiamat Rod and the Justice Sword.  Tiamat Rod can be equipped by Masqurin, Grace and Noon, and grants the Tiamat spell to the user.  Weapons level for the Rod will determine if the character can use Tiamat LV2 or only Tiamat LV1.  Justice Sword can be equipped by Synbios (Eldar and Fynnding: CAN'T EQUIP).  At LV3 Sword AND LV3 Blade, the Photon Blade scores 1 more damage point than the Justice Sword, but I suggest carrying both and alternating. When you finally have these items, head back to Malorie to revive fallen friends, get other Mithril Weapons, deposit or sell useless/spare items and re-organize your party. 
The Final Battle

To be ready for the final battle, here are a few tips:

1- Hire a mercenary.  I suggest the Knight (Elric), for he has interesting Special Attacks and is quite strong.  If you don't have all the bonus characters, you can hire more than one.  The hired mercenary(ies) will fight with the second party at the Dam; If your whole Force is composed of ALL available characters (19 including Fynnding), you can hire only one mercenary.  If you have less fighters, you can yave more mercenaries (18 characters: 2 mercs ; 17 characters: 3 mercs ; 16 characters or less: 4 mercs ) .

2- The party that will head for the Dam is composed of the characters in reserve, so I hope you trained them too !  I suggest having long-range hitters (spells, arrows, shurikens) in the main party and fast movers (Eldar, Fynnding, Frank) in the second party.  Also have at least one healer in each party.  Use the Friendship system wisely to choose who goes where.

3- Before defeating GigaBreaker at the Dam, be sure all your characters fighting the Colossus have already reached the safety zone (in front of the castle door) or that they could get there in one move.  All characters who will not be in the safety zone will be carried away by the water release, thus considered dead, so they cannot be used in the battle against Arrawnt.  So even if it offers a big target for the Colossus, position your characters in front of the door and side-by-side.  Anyway, if the Colossus hits you with a X-Spark, the damage will be distributed among all targets...