Fragile Eyestalks.  If an eyestalk is attacked (attacks against a eyestalk have disadvantage) and suffers more than 50 points of damage from a single turn the eyestalk can be severed from its body.

Bite (Chilling Bite). Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit:  (2d6 + 7) piercing damage plus 1d6 cold damage.

Tongue Attack (Vile Tongue). Ranged Weapon Attack: +9 to hit, reach 15 feet, one target. Hit: (2d10 + 9) bludgeoning damage plus 1d8 acid damage. The target must make a DC 17 strength check or be grappled by the tongue and pulled in front of the beholder. Success means they are not grappled and take half damage. Failure means they take full damage and will also have to make a save against his central eye aura next round.

Central Eye (Psychic Blast Aura). Upon coming in contact with the central eye's aura cone (60 foot cone radiating from the front of the creature), the player must make a intelligence saving throw. If they fail they suffer 2d12 psychic damage and are confused (as per umber hulk's confusing gaze) until the next round. On a success they suffer half damage and no confusion. At the start of the next round the player can choose to avert their eyes to avoid this effect but then will suffer disadvantage on any attack rolls until they move out of the eye's cone. 

Eye Rays. The spectator shoots up to two 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.

• Top Right Eyestalk (Frost Ray). This eyestalk fires a deep blue ray of cold in a wide arc that deals 6d6 cold damage to anyone within a 30 foot radius of the point of impact. The saving throw for this is DC 16 dexterity. 
• Top Left Eyestalk (Ice Beam). This eyestalk fires a whitish blue cold energy beam that deals 2d4 force damage and 2d4 cold damage to anyone in a line (it pierces targets) of 60 feet. The saving throw for this is DC 16 Dexterity
• Bottom Right Eyestalk (Ray of Frozen Dominion). This pale white beam strikes a single target who must then make a DC 16 charisma saving throw or be dominated for 1 round. (if the target has already have their round, it lasts through their next round). In addition the player emits a chilling aura doing 2d4 damage to them and anything within 15 feet. 
• Bottom Left Eyestalk (Beam of Cold Siphoning). This greenish blue, teal colored beam strikes a single target and deals 3d10 cold damage on a failed DC 15 con save (half as much on a save) in addition it returns that damage as health back to the Ice Tyrant as it pulls the water from the players body and converts it to ice which heals the creature. 

Spell Reflection. (Reflected in Ice)  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.

The Ice Tyrants gets 3 legendary actions per round of combat. It can do its eye attacks, a bite, a tongue attack or one of several special legendary actions.

Quadra Beam. (Recharge 6, can only be done with less than 50% hp) Zalanar focuses all his eyes on one target. all its eyes forming a central beam directly in front of its large central eye before the central eye pushes the beam out at intended target. This freezing cold beam will strike a single target, piercing through for up to 120 feet in a straight line. On a failed save the target suffers 5d20 cold damage. If the target drops to zero hitpoints from this they are frozen solid. On the following round they must make another saving throw. If they fail they shatter into pieces and die instantly. The DC for this is Dexterity DC 18. The save when frozen is Constitution DC 15. A frozen target can be melted out of the ice. The ice has a HP of 40 and takes double damage from fire but is immune to cold. 

Triangle Blast. (Recharge 5-6, can only be done with less than 50% hp) Zalanar focuses three of his eyes on a central point and the three beams create a cold blast which detonates at the target location dealing 4d12 cold damage in a 20 foot radius. If the targeted player (not players in the radius) fails their save they are frozen solid.   On the following round they must make another saving throw. If they fail they shatter into pieces and die instantly. The DC for this is Dexterity DC 18. The save when frozen is Constitution DC 15. A frozen target can be melted out of the ice. The ice has a HP of 40 and takes double damage from fire but is immune to cold. 

Fan of Ice. (Recharge 4-6, can only be done with less than 50% hp)  Zalanar uses his two eyes to sweep 180 degrees in front of him in a fan like shape, 50 feet out from his location. Anyone in this half circle takes 3d10 cold damage. The ground here is difficult terrain and movement here is halfed. Players that fail their save slip on the sheet of ice that is created on the ground and are knocked prone for a round. 

Ice Meteor. (1/day, can only be cast with less than 25% hp) Zalanar uses the round to focus his eyes in front of his large central eye. He begins to craft a massive meteor of pure ice. This is a concentration spell. Zalanar must make a concentration check (DC 15) if he takes more than 50 damage in a single attack. The following round on his turn Zalanar will launch the frozen meteor at a target location within 200 feet. It will impact with a radius of 50 feet and deal 5d12 cold damage and 5d12 bludgeoning damage. The save is a DC 18 dexterity save.