Immutable Form: The golem is immune to any spell or effect that would alter its form.

Magic Resistance: The golem has advantage on Saving Throws against Spells and other magical Effects.

Magic Weapons: The golem's weapon attacks are magical.

Legendary Resistance (3/Day): If Zeep-zap the gate guardian fails a saving throw, it can choose to succeed instead.
 

Spellcasting.  Zeep Zap The Gate Guardian  is a 6th level spellcaster. Its spellcasting ability is [intelligence] (spell save DC 17, +8 to hit with spell attacks). Zeep Zap The Gate Guardian has following [Wizard] spells prepared:

Cantrips (at will): fire bolt, acid splash
1st level (4 slots): grease , burning hands

2nd level(4slots): Scorching ray,  Misty step

3rd level(3slots): Counterspell, Lightning bolt

4th level(3slots): fire shield, polymorph

5th level(2 slots): conjure elemental ,Geas

6th level(1 slot): Eyebite

Multi attack: the Gate Guardian can make four melee attacks, cast a spell before making three melee attacks or ranged attacks, or make two ranged attacks before making two melee attacks.

Talon swipe. magic dagger attack: +14 to hit, reach 5 ft., 1 target. on Hit: (3d6 + 3) [slashing] damage and (3d6+6) [piercing] damage)

Spit fire. Ranged Weapon Attack: +12 to hit, range 15/30 ft., 1 target. Hit:  (1d10 + 6) [fire] damage and 1d10+6 [bludgeoning] damage 

As a bonus action the gate guardian may attempt to cover itself more with its wings, increasing its ac by 2 until its next turn, but putting it at disadvantage on dexterity checks until its next turn.

Frightening roar. The gate guardian releases a feral roar in an attempt to intimidate any who oppose it. all creatures currently engaged in combat with the gate guardian must succeed on a dc 16 wisdom saving throw or be frightened. this save can be repeated after a failure by a player at the start of that players turn.

Can take 3 Legendary actions choosing from the options below. Only one legendary action can be used at a time, and only at the end of another creature's turn. Spent legendary actions are regained at the start of each turn.

Forced regeneration (Costs 1 Action): The gate guardian is able to heal itself from massive injures at will. it can do this a total of three times before it needs a long rest The gate guardian heals itself for 6d10 health with a minimum of 30 points.

Counter spell (costs 3 actions) : The gate guardian counters a spell that targets them directly.

Defensive Gust (costs 2 actions) : The gate guardian beat's their wings, all creatures in front of them must pass a dc 23 dexterity save as magical winds blow them back 30 feet. on a success creatures are knocked prone in place.

Enter the description for how mythic actions work for your monster here.

Mythic Action Name (Costs # Actions). Enter the description for your mythic action.