Monster Den (Wolfen) x2
Monster Den (Ampelar) x1
Alright, this battle is TOUGH. The enemies are strong, and most can use powerful magic. You may need to level up a bit before you're able to make it through this one. In addition, you need to work quickly, or else the dens will start spawning Wolfens, which is BIG trouble.
You'll notice two Ampelars and two Wolfens beyond a canyon to the right. As tempting as it is, don't approach them! If you do, you'll likely pack the canyon with your troops, and the Wolfens will each cast Torneda which will probably kill everyone. Instead, on your first round, huddle everybody together, away from the enemies from the north to the south. This will force them to approach you on the second round, where you will be able to strike first. The faster you eliminate the Wolfens, Ampelars and Manticores, the better.
After the first wave, you'll need to worry about the Totelices and K'thons. And these guys are very, very dangerous, especially the Totelices. Lightning-based spells are very useful here, so use Laizaza if you have it. If you can move Rolan in position where the eastern group of enemies are visible too, you might consider casting Krulain to thin them out a bit. Try to at least gain access to the island as quickly as possible so you can unarm the den before Ampelars start coming out.
Once you have secured the island, send an army or two to the west to close off the dens there. These dens spawn Wolfens, so neglecting them could be very dangerous. Hopefully, you'll be able to get them closed off before too many Wolfens come out. At this point, you should be pretty close to finishing the battle, so kill off any surviving enemies.
A big part of this battle is luck, and there's not much you can do if your generals start getting killed off by instant-death spells. If at first you don't succeed, try, try again.