Mimicry.The Vivid Rupter can mimic animal sounds and humanoid voices. A creature that hears the sounds can tell they are imitations with a successful DC 14 Wisdom (Insight) check.

Spellcasting. The Vivid Rupter is a 3-level spellcaster. Its spellcasting ability is 15 (spell save DC 14, +4 to hit with spell attacks). The Vivid Rupter has following bard and wizard spells spells prepared:
Cantrips (at will): vicious mockery, mold earth, firebolt, poison spray
1st level (5 slots): shield, magic missile, cure wounds 

Hideous Sting. Melee Weapon Attack: +4 to hit, reach 5 ft., 1 target. Hit: 4 (1d4 + 2) piercing damage, the target must make a DC 10 dexterity saving throw or each time the target uses its movement, its movement is halved (until the creature makes a short or long rest). 

Poison Short Bow. Ranged Weapon Attack: +4 to hit, range 50/150 ft., 1 target. Hit: 7 (2d4 + 2) piercing damage. On hit the poison short bow deals another 1 poison damage and the creature makes a DC 12 constitution saving throw or be knocked unconscious but stable. 

Invisibility (4/day).The Vivid Rupter magically turns invisible until it attacks or casts a spell, or until its concentration ends (as if concentrating on a spell). Any equipment the Vivid Rupter wears or carries is invisible with it.

Invisiblity (1/day). once per day the Vivid Rupter may become invisible until the Vivid Rupter makes an attack or casts a spell or until concentration ends (as if concentrating on a spell). Any equipment the Vivid Rupter wears or carries is invisible with it.