Watcher

The Watcher is invulnerable while in its invisible form. It's a rare occurrence for a Watcher to show itself but only if it feels it's under threat or if forced out. The Watcher cannot bite while invisible but is able to transmit thoughts. 

Bite. Melee Weapon Attack: +1 to hit, reach 5 ft., one target. Hit: 2 (1d6 − 1) piercing damage.

Transmit Thoughts The Watcher projects its experiences into one or two creatures it can see within 90 feet of it. It can use two different experiences on a turn.

1. Confusion. The target must succeed on a DC 13 Wisdom saving throw, or it can’t take reactions until the end of its next turn. On its turn, the target can’t move, and rolls 1d10. If the target rolls 7-10, they inflict 1d6 bludgeoning damage on themselves. Otherwise the target uses their action to make a melee attack against any random target in range.
2. Torment. The target must succeed on a DC 13 Intelligence saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
3. Fear. The target must succeed on a DC 13 Charisma saving throw or be frightened for 1 minute. The target can repeat the saving throw at the end of each of its turns, with disadvantage if the Watcher is visible to the target, ending the effect on itself on a success.

Spell Reflection. If the watcher makes a successful saving throw against a spell, or a spell attack misses it, the spectator can choose another creature (including the spellcaster) it can see within 30 feet of it. The spell targets the chosen creature instead of the spectator. If the spell forced a saving throw, the chosen creature makes its own save. If the spell was an attack, the attack roll is rerolled against the chosen creature.

Magical Weapon Absorption. If the watcher is targeted by a magical weapon and the attack misses, the watcher is able to absorb the magical power of the weapon and use it as an attack on its next turn dealing damage equal to the weapon's attack.