4 Rangers, 4 Spellblades, and 2 Dark Flans. In total, there are 6 dark enemies with negative magic and light resistances, and 4 Fire enemies weak to water.
All of the enemies are somewhat closely grouped together in the main area, front of the spawning location. However, the team's spawn location are split into 2 sides. Units in slot 1, 2, and 5 are closer to the left side, while 3, 4, and friend unit are closer to the right side.
Strong light mage damage dealers like Yuna and/or Sakura are the unit of choice here. With a lot of Rangers and Spellblades, you'll still need to bring a tank, and recommended to have some missile or slash resistances. If your units aren't strong enough, you might need a tanker on both sides of the area.
The Dark Flans have very high HP, but they mostly tend to do group heals instead. If they attack, it's usually a poison related attack. Bring some antidotes, or a healer to help with the fight if you're struggling.