Final Fantasy Tactics Walkthrough

This battle can be extremely difficult or extremely easy, depending on your luck.  Delita will be in danger early because he's ready to rush after Tietra, but this means he'll instantly be in trouble. Establishing and equipping him as a Knight can help some here, and if he withstands, dodges, or blocks some of the attacks in the first turn or two, then you're in good shape.

That said, this is a dangerous battle because all of the standard enemies are tough physical fighters who are hard to avoid due to the claustrophobic map layout, and Wiegraf has very strong and ranged and area-of-effect sword skills that you haven't faced before. It's difficult to spread out, but if you allow more than one or two units to get hit on each of Wiegraf's turns, you may find yourself dead pretty quickly. On top of that, Boco the chocobo has a big move radius and the ability to heal his mates.

At this stage, Monks and Knights are your best bets for hitting Wiegraf, but it's likely you'll need to hit him from the side or the back because he has a high chance of evasion or blocking.  A Black Mage will help out immensely, and you'll definitely need two or more people with the ability to use items, specifically Phoenix Down because one of Wiegraf's skills has a chance of adding KO status instantly.  Focus on Wiegraf, because driving him to critical HP ends the battle, but don't be too rash - keep an eye on the most likely danger to your party at each turn, as too much tunnel vision can let the other enemies through your defenses.

Wiegraf will teleport away from the battle and Delita and Ramza enter the windmill.  Tietra is gone, as Gragoroth has defied orders again and kept his hostage.  Delita wonders aloud when they'll finally get her back, and they move onward to Ziekden Fortress.