This crystal device is usually about 4 square feet in area, framed in metal, wood, etc. 

It is usable only by magic-users, although it can be affixed to a surface to operate alone by giving a command word. 

A mirror has from 13 to 18 non-spatial/extra-dimensional compartments within it.

Any creature coming within 30-ft of the device and looking at it so as to see its reflection must save versus magic or be trapped within the mirror in one of the cells. 

It is 100% probable that any creature not aware of the nature of the device will see its reflection, the probability dropping to 50% if the creature actively avoids so doing and 20% if the creature is aware that the mirror traps life. 

When a creature is trapped, it is taken bodily into the mirror. Size is not a factor, but automatons and non-living matter (including golems but excluding intelligent undead) are not trapped. 

The possessor of the mirror can call the reflection of any creature that is trapped within to the surface of the mirror, and the powerless creature can be conversed with. 

If mirror capacity is exceeded, 1 victim (random) will be set free in order to accommodate the latest one. 

If the mirror is broken, all victims are freed usually to then attack the possessor of the device). 

Note that the possessor of a mirror of life trapping can speak a command word so as to free a trapped creature, but the cell of the creature must be known. Example: "In the name of Zagig the Great I command the occupant of the 3rd cell to come forth!"