Many Eyes. The Spectator is immune to being Flanked.

Multiattack. The spectator can make one Bite attack and two Eye Ray attacks, or three Eye Ray attacks.

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

Eye Rays. The spectator shoots one of the following magical eye rays at one or two creatures it can see within 90 feet of it. It can use each ray only once on a turn.

• Confusion Ray. 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 it uses its action to make a melee or ranged attack against a randomly determined creature within range. If the target can’t attack, it does nothing on its turn.
• Paralyzing Ray. The target must succeed on a DC 13 Constitution 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.
• Telekinetic Ray. If the target is a creature, it must succeed on a DC 13 Strength saving throw or the spectator moves it up to 30 feet in any direction. It is restrained by the ray’s telekinetic grip until the start of the spectator’s next turn or until the spectator is incapacitated.

If the target is an object weighing 300 pounds or less that isn’t being worn or carried, it is moved up to 30 feet in any direction. The beholder can also exert fine control on objects with this ray, such as manipulating a simple tool or opening a door or a container.

• Wounding Ray. The target must make a DC 13 Constitution saving throw, taking 16 (3d10) necrotic damage on a failed save, or half as much damage on a successful one.

Bonus Actions. Along with its normal multiattack, the spectator may take one Bonus Action, if the conditions are met.

• Hey! You stole my flowers! The spectator gets one free eye ray attack against any creature holding a bunch of petunias.
• You’ve got something on your face… here, let me get it for you. The spectator licks a target in melee range. If the target fails a CHA (DC 13) saving throw, they are stunned until the spectator’s next turn.

Create Food and Water. The spectator magically creates enough food and water to sustain itself for 24 hours.

Spell Reflection. If the spectator 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.

Oh my, you appear to have stepped in something… As a reaction to someone moving, glues their feet to the ground, cancelling their movement for that round. Also that person’s feet smell as if they stepped in something for the next 1d8 hours.

What a lovely bunch of petunias! On being attacked, Turns the weapon into a bunch of flowers for a round

Yummy! The spectator “catches” a spell that is cast at it, and eats it. Can use that spell as a central eye attack next round. (The spell still effects the spectator normally)

Intruders! The spectator creates an invisible wall around the forge of spells, preventing creatures from accessing the items or mechanisms in that area. This may trap a creature inside the wall. The spectator must make concentration checks to maintain the wall. It makes these checks when the wall or the spectator are attacked.

What dreadful weather we’re having. The spectator causes a rainstorm to begin in the cavern, making the stone difficult terrain and lightly obscuring anything 20ft or further away. Also conjures a pink umbrella that follows the spectator around and makes it immune to these conditions.

I’m bored, let’s shake things up a bit! Everyone must make a DC 15 INT saving throw. All who fail (and the spectator) are teleported to locations of the spectator’s choice. The spectator may only choose locations that are currently occupied by one of those creatures, and cannot place two creatures in the same space.

You dropped some magic! Here, you can have it back! The spectator emits scintillating magic in a 20ft cone, which deals Xd6 force damage on a failed DEX (13) save and half as much on a successful save, where X is the number of attacks with spells and magic weapons that have hit the spectator. This attack triggers a roll for a wild magic surge if it hits a wild magic sorcerer.

I’m afraid I have to leave now, but you’ve been terribly pleasant company! The spectator opens a gateway to the dark between the stars, a region infested with unknown horrors. A 20-foot-radius sphere of blackness and bitter cold appears, centered on the spectator and lasting for the duration. This void is filled with a cacophony of soft whispers and slurping noises that can be heard up to 30 feet away. Darkvision does not operate in this area, but light sources do provide light.

The void creates a warp in the fabric of space, and the area is difficult terrain. Any creature that starts its turn in the area takes 2d6 cold damage. Any creature that ends its turn in the area must succeed on a Dexterity saving throw or take 2d6 acid damage as milky, otherwordly tentacles rub against it.