Source: 13 Ghosts (the remake)
Location: Funky glass house
Threat Assessment: 8. They are trapped so if you aren't in the house you are cool. EXCEPT, they are part of a diabolic machine that will grant the person that works it all the power he wants which means you is boned to the stones. If you are in the machine they are invisible without special glasses and can reach out and touch you, that is kill you good.
Limitation: They have to follow the rules. Spells can be used to ward them off.