The concept is simple, build your dungeon, set up rooms from lair to casino, attract more demons, create traps then wait for those so call ‘Heroes’ to show up. This game will exercise your inner evil, instead of worrying about how to defence your lair, your primary concern would be how to cook them this time Kill them and raise them as mindless skeleton, capture them and put in the pit for training, or torture them and convert them to your side
And if your minions can't do the job right, you can possess them and change the interface to First person view and do the deed yourself