These Acorn Fellows are known for their tough shells and hard cores. They are considered to be invincible and cannot be killed easily. 

Longsword. +2 to hit, reach 5 ft., one target. Hit: 2 slashing damage.

Longbow. Ranged Weapon Attack: +5 Hit: 1 piercing damage, and the target must succeed on a DC 11 Constitution saving throw or become poisoned for 1 minute. If the saving throw is lower than 6, it will fall unconscious for 2 minutes.

Emotionally Connected. The acorn touches a creature and magically knows the creature's current emotional state. If the target fails a DC 10 Charisma saving throw, the acorn also knows the creature's alignment. Celestials, fiends, and undead automatically fail the saving throw.

Invisible. The sprite magically turns invisible until it attacks or is attacked. Any equipment the acorn wears or carries is invisible with it.