When we started designing the hostile NPC encounters for The Chronicles of Spellborn (TCoS), we worked towards a system that mimics real live hostile behavior as much as possible. We didn't want to just 'randomly' place mobs on the maps that would simply react to agro and start their melee routine or throw some fireballs. In order to achieve this goal and still be able to populate the massive world that is required for a MMO, we broke each NPC encounter down in 5 components that together define the behavior of hostile NPCs.

1. Faction
2. Group
3. Class
4. Attack pattern
5. Level