Monster Magic Treshold
A monster equipped with magic items can use the powers those items grant.
Enhancement Bonuses: A monster benefits from an enhancement bonus to attack rolls, defenses, or AC only if that bonus is higher than its magic threshold, as shown on the table below.
A monster’s magic threshold is an abstract representation of its equipment, power, and general effectiveness against characters of its level. If you give the monster a magic item that grants a bonus to attack rolls and damage rolls or to defenses, subtract the magic threshold from that bonus before you apply it.
For example, if you give that 8th-level ogre savage a +2 magic greatclub, you add only a +1 bonus to its attack rolls and damage rolls, since its magic threshold is +1
|Monster Level||Magic Threshold|
Published in Dungeon Master's Guide, page(s) 174.