Sidequest: Colliery Investigation, Beowulf, and Reis

This battle can be difficult because all of the Chemists are equipped with Mythril Guns that do a lot of damage and have good range. You'll want to bring someone like Agrias or even better, Orlandu, to hit them from range and do a lot of damage. Summoners are okay here, but someone with Holy is even better. Make sure you can heal damage and revive people, because they can go down pretty quickly if they're targeted by multiple Chemists.

The sightlines of this battle make it tricky, but you can use it to your advantage by taking out the enemy in places where it is hard for their companions to heal them. Focus your attacks on a single enemy at a time, because you'll want to try to take one out each turn to avoid a large round of healing. Even better if you can get your party into blocking positions so that healing (or reviving!) is impossible.

You will want to move fairly quickly up the ramp to take out the upper force before they can cause too much damage below. Beowulf will perform well as a guest in this battle, though you may end up wanting to knock him out if you want to farm this battle.

Steal the Chemist's Blaze Gun in this battle! Depending on when you start this quest, it might be your first chance at a magical gun, like Mustadio described in a cutscene just after meeting him. If that Chemist is the last enemy left, you may have to kill Beowulf so he doesn't end the battle first, but you definitely want this gun as spell guns are few and far between.

This battle is pretty simple, just take out the monsters first when they get close, as they are the most powerful, then Thief 1 and Thief 2, and the Chemist once you've gotten his gun away from him. Having more than one person capable of stealing is handy so you can gang up on the Chemist and more quickly get the weapon.

Again, Holy works nicely, and having someone to heal is a definite must, due to the threat of the monsters and their powerful physicals.

Nothing much new here aside from the dragons. The Blue Dragons will definitely be your first targets because of their massive ice attacks that have extended range - as you'd expect, fire works nicely on them. Unfortunately, the higher-leveled fire attacks take much longer to charge, so you're better off using Holy or even Flare. If you're using sword-wielding characters, there is a good chance you've got Ice Brands equipped depending on when you take this quest - if you don't fix that before the battle they'll be useless against those dragons.

After the dragons, take out the Chemists, and after that, try to invite the Uribo into your party so you can poach its offspring. If you haven't done this before, you will need to bring along a Mediator and use the Invitation ability and keep the piggy on your side until the end of the battle. This shouldn't be too much of a difficult battle if you have a healer and equip properly to handle the dragons.

You'll start off in a disadvantaged position, with the main route to the scene of the battle likely blocked by a high wall. The best thing you can do is to give as many people as possible Ignore Height so you can get to Reis faster. If you can't do this, start your best movers and fastest characters at the back of the formation so they can make more progress towards the front lines.

Reis will take out many of the enemies on her own but will eventually need backup, and the faster you can get Ramza or Orlandu over there, the better. She'll take a beating but she's got good HP, and the damage dealt to her is low due to her Brave and Faith stats. Holy's range will come in handy here, especially since the Archaic Demon is weak to it. That said, defending Reis is the objective of the battle, so don't leave her alone too long lest she become endangered. Focus on getting your units to places where they can keep Reis safe, including getting a healer into position if you can't end the battle quickly.

There are fun monsters here to try to invite if you feel like it, too.

Following the battle, it turns out that Reis is who Beowulf was looking for in the first place. You'll have the opportunity to recruit both of them permanently - do it. Even if you don't want them, further sidequests require them to be in your party. You'll also get the stone you'll need for that fancy machine you left in Goug, so that's your next stop in continuing your sidequests.