Interactive NPCs (non-playable characters)

1. PvP (Player vs Player) vs PvE (Player vs Environment) (Player-Centric Gamification Tips)
2. Open World vs Closed World (Player-Centric Gamification Tips)
3. Avatars vs Characters (Player-Centric Gamification Tips)
4. Player Roles vs Player Classes (Gamification Achievement Systems Tips)
5. Game Respawn vs Game Revive (Player-Centric Gamification Tips)
6. Player Market vs Game Market (Virtual Economy Gamification Tips)