Bones-to-dust Elf

Broken. This is broken on purpose and I have no idea why anyone in their right minds would ever want to use or allow it, I just wanted to make something utterly broken to scare my party when they snoop through my homebrew.

Magic Resistance. The archmage has advantage on saving throws against spells and other magical effects.

Spellcasting. The archmage is an 18th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 18, +10 to hit with spell attacks). The archmage can cast disguise self and invisibility at will and has the following wizard spells prepared:

Cantrips (at will): fire bolt, light, mage hand, prestidigitation, shocking grasp

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

2nd level (3 slots): detect thoughts, mirror image, misty step

3rd level (3 slots): counterspell, fly, lightning bolt

4th level (3 slots): banishment, fire shield, polymorph

5th level (3 slots): cone of cold, scrying, wall of force

6th level (1 slot): globe of invulnerability

7th level (1 slot): teleport

8th level (1 slot): mind blank*

9th level (1 slot): true polymorph

*The archmage casts these spells on itself before combat.

Dagger. Melee or Ranged Weapon Attack: +6 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 4 (1d4 + 2) piercing damage.

Turn your bones to dust. 3/Day. Target one non-fey creature within 300 feet which must succeed on a DC: 18 constitution saving throw or have it’s bones turned to dust. 
On a failure: the target is considered restrained and falls prone. A spell such as greater restoration or remove curse may restore the creatures bones.