Outcast's Path

Is it normal that on the first week of the second month, a yellow faction invades with a sizable army containing many demons, etc.? It's a strange RPG.

I was talking about an active opponent. Ideally, they should harass the hero throughout the game to keep them on their toes. But the yellow faction can't enter cities or other areas of the map, nor can they interfere with quests, which the hero can take advantage of. However, they will definitely hunt down the dark elf castle underground.
What difficulty level are you playing on?

The yellow faction only has one hero, but they will appear multiple times.

Added 3 minutes later
The yellow faction has a castle, from which they receive good reinforcements. If you destroy it, you can make your life a little easier.