This is similar to the Karmen Fortress in the Usso Forest mission, except there are more enemies and the buildings have more health. You'll want to knock down the buildings quickly, because Karmen ranged units will continue to at firing at you from behind the protection of towers, stone walls, and fortresses.
Luckily, there is a potion that fully heals your army about halfway through.
It seems that enemy units in the second half deal more damage and you will almost always find Steel equipment, and sometimes Iron equipment. If you are tired of using Iron weapons, you may want to replay this mission for some extra materials.
When you beat this mission level a second time, you will obtain the Lv.1 egg of Ejiji Cliff Fortress Siege. Steel level equipment is dropped by the Karmens occasionally.
After winning the level, a repeatable version appears occasionally and stays until it is beaten.