Defeating the dirge bard shouldn't have been too difficult. Your party waited until he was alone, strumming idly on his mandolin, to strike. The problem is, that this bard is never alone. The rogue's sneak attack was caught halfway by the mandolin's suddenly animated neck twisting around their arm. The instrument's strings screamed along with the dirge's thunderous spell sending the fighter bouncing across shattering cobblestone. The dirge isn't even playing anymore but the fast tempo keeps on. He's moving quicker than he should, casting spells on the go. Now the mandolin has sprouted teeth and is chewing on the rogue. Yep, it's going to be a rough night.

Unsurprisingly, the first strumming mimic was crafted by a bard seeking a way to make a companion and self-playing instrument rolled into one. Just as unsurprisingly, that bard ended up being one of his creations' first meals. Since then, the strumming mimics have realized they need musicians to easily travel from hunting ground to hunting ground. As such, they tend to bond to players with a more chaotic and bloodthirsty bent. A few of these monstrosities have even convinced middling bards that they must be continuously supplied with victims if that bard wants to keep their newfound 'skill' and fame. Strumming mimics have a hereditary fear of fiddler mimics. Strumming mimics know that those superior predators can devour them with ease to keep a hunting ground all to themselves.

Strumming Mimic

Small Monstrosity (shapechanger), neutral

Armor Class 12 (natural armor)

Hit Points 58 (9d6 + 27)

Speed 15 ft

Str 14 Dex 12 Con 16 Int 7 Wis 12 Cha 16

Skills Performance +5, Stealth +5

Damage Resistances thunder

Damage Immunities acid

Condition Immunities prone

Sensesdarkvision 60 ft, passive Perception 11

Languages understands Common and Elvish but cannot speak

Challenge 3 (700 XP)

Shapechanger.

The mimic can use its action to polymorph into a mandolin or back into its true, amorphous form. Its statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.

Accompaniment (Object Form Only).

When played by a creature, the mimic provides Advantage on Charisma (Performance) checks as well as +1 to the spell DC of any spells that deal Thunder damage.

Adhesive (Object Form Only).

The mimic adheres to anything that touches it. A Large or smaller creature adhered to the mimic is also grappled by it (escape DC 12). Ability checks made to escape this grapple have disadvantage.

False Appearance (Object Form Only).

While the mimic remains motionless, it is indistinguishable from an ordinary mandolin

Grappler.

The mimic has advantage on attack rolls against any creature grappled by it.

Actions

Pseudopod.

Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 6 (1d8 + 2) bludgeoning damage. If the mimic is in object form, the target is subjected to its Adhesive trait.

Bite.

Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 6 (1d8 + 2) piercing damage plus 4 (1d8) acid damage.

High Note (Recharge 6).

A wave of thunderous force sweeps out from the mimic in a 15-foot cone. Targets in the area of effect must succeed on a DC 13 Constitution saving throw. On a failed save, a creature takes (13) 3d8 thunder damage and is pushed 10 feet away from the mimic. On a successful save, the creature takes half as much damage and isn’t pushed. In addition, unsecured objects that are completely within the area of effect are automatically pushed 10 feet away from mimic. This action emits a musical chord audible out to 300 feet.

Bonus Actions

Bassline.

If the mimic succeeds on a DC 13 Charisma (Performance) skill check, it and all of its allies within 20ft may make an additional Bonus Action to Dash, Hide, or Use Object until the beginning of the mimic's next turn. In addition these creatures have Advantage on saves against Charm or Fear-based effects.