Crystal Mephit

Death Burst. When the mephit dies, it explodes in a burst of psionic energy. Each creature within 5 feet of it must make a DC 10 Wisdom saving throw, taking 4 (2d4) psychic damage on a failed save, and the target has disadvantage on the next attack it makes before the end of its next turn.

False Appearance. While the mephit remains motionless, it is indistinguishable from an ordinary crystal shard.

Innate Spellcasting.(1/Day). The mephit can innately cast faerie fire (spell save DC 10), requiring no material components. Its innate spellcasting ability is Charisma. 

Claws. Melee Weapon Attack: +3 to hit, reach 5 ft., one creature. Hit: 3 (1d4 + 1) slashing damage plus 2 (1d4) psychic damage.

Force Beam (Recharge 6). The mephit exhales a 30- foot line of pure magical energy. Each creature in that line must succeed on a DC 10 Dexterity saving throw, taking 5 (1d10) force damage on a failed save, or half as much damage on a successful one.