Callous the Glutton

Spellcasting. The mage is a 9th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 14, +6 to hit with spell attacks). The mage has the following wizard spells prepared:

Cantrips (at will): eldritch blast, light, mage hand, prestidigitation

1st level (4 slots): detect magic, mage armor, magic missile, shield

2nd level (3 slots): misty step, darkness

3rd level (3 slots): counterspell, fireball, blink

4th level (3 slots): greater invisibility, ice storm

5th level (1 slot): cloudkill

Dagger. Melee or Ranged Weapon Attack: +5 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 4 (1d4 + 2) piercing damage.

Mindmaster's Monocle
Wondrous item, very rare (requires attunement by a wizard)

This ancient golden monocle's lens is a roughly hewn ruby. While you wear this monocle, it magically floats in front of your eye, instead of resting on your face, and you can see clearly through its ruby lens. While peering through the lens, you always know if a creature you can see is concentrating on a spell. You perceive a concentrating creature's head as being shrouded in an indigo mist.

This monocle has 10 charges for the following properties. It regains 1d6 + 4 expended charges daily at dawn.

Spells. While wearing the monocle, you can use an action to expend some of its charges to cast one of the following spells from it, using your spell save DC: arcane eye (4 charges), detect thoughts (2 charges), or telepathic bond (5 charges).

Mental Assault. While wearing the monocle, you can use a bonus action to expend 3 of its charges to attempt to break a creature's concentration on a spell. The target must be within 60 feet of you, and you must be able to see it. When you do, make an Intelligence check contested by the target's spellcasting ability check. If you win the contest, the target's concentration on the spell ends.