Grimmlet

Reproduce. When a grimmlet takes damage from a spell and isn't reduced to 0 hp, a number of new grimmlets equal to the spell's level appear in unoccupied spaces within 10 feet of the grimmlet. If the spell is a cantrip, only one grimmlet is created. Sixteen or more grimmlets within 30 feet of each other can use their reactions to come together and form a grimmlet swarm in a space within 5 feet of one grimmlet.

Self-destruct. When the grimmlet dies, it explodes in a spray of Void-infused crystal shards. Each creature within 5 feet of the grimmlet must succeed on a DC 12 Dexterity saving throw or take 3 (1d6) slashing damage and 3 (1d6) psychic damage. Grimmlets damaged by this trait don't Reproduce.

Innate Spellcasting (Psionics). The grimmlet's innate spellcasting ability is Charisma (spell save DC 12, +4 to hit with spell attacks). It can innately cast the following spells, requiring no components: At will: crushing curse, minor illusion 3/day each: maddening whispers

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