Source: Sword & Wizardry Monstrosities
A Mirror Fiend is a haunted object which traps the soul of the unsuspecting. A demonic being lurks within it's own pocket realm inside the mirror. As you enter the abandoned house your eyes dart across the room. What should be your reflection appears to be something else. A human head glances back at your. You feel a tug at your soul as if it's trying to rip it from your body.
Those of weak will have their souls torn from their body. Their physical body remains staring at the mirror while their spirit fights the fiend inside the mirror. A false move by fellow adventurers can spell doom for the trapped. If your comrades destroy the mirror your soul is trapped. If they decide to move your body you lose control of your soul while battling the mirror fiend inside it's realms. That leads to death as the Mirror Fiend tears your soul apart as you are immobile.
Combat: The Mirror Fiend is Challenge Level 10. The physical mirror can be shattered from the outside and spells reflect back at caster if they target the mirror. The Mirror Fiend has a trap the soul ability. Once you glare at the mirror you must make a save. If you fail the save your soul is torn from your body and into the mirror.
Once you are inside the mirror you suffer a -4 to attacks due to being unfamiliar with your surroundings. Each round reduces the penalty by 1. They Mirror Fiend is immune to non-magical weapons and has 50% magic resistance. In this mirror realm you must defeat the fiend to return to your body. As stated above your physical body is in a fragile state. False moves by your party can kill you.
The Mirror Fiend is rather dangerous monster since the tactics of your party can determine success or failure. This can be a nasty encounter that might give some players hard feeling afterwards.
- Mirror Fiend: HD 8; AC 3 ; Atk 1 mirror weapon (3d4); Move 12; Save 8; AL C; CL/XP 10/1400; Special: Unaffected by normal weapons, 50% magic resistance.