Spellcasting. The mage is a 20th-level spellcaster that uses Intelligence as its spellcasting ability (spell save DC 22; +14 to hit with spell attacks). The mage knows the following spells from the wizard’s spell list:

Cantrips (at will): eldritch blast, friends, shocking grasp, hellfire, infestation, mold earth, word of misfortune

1st Level (4 slots): disguise self, mage armor, protection from evil and good, shield

2nd Level (3 slots): shatter

3rd Level (3 slots): counterspell, dispel magic, ride the rifts, shadow portal

4th Level (3 slots): delerium blast, knife of fate, raulothim's psychic lance, ride the lightning, stellar bodies, vitriolic sphere

5th Level (3 slots): cone of cold, living shadows, negative energy flood, synaptic static

6th Level (2 slots): chain lightning, circle of death, disintegrate, mass suggestion, otto's irresistible dance

7th Level (2 slots): finger of death, power word pain, prismatic spray

8th Level (1 slot): maddening darkness

9th Level (1 slot): blade of disaster

Fade Away: While standing perfectly still, you can use an action to become invisible. You become visible again if you move or take an action. You can use this feature a number of times per day equal to your proficiency bonus.

blade of disaster

shield

Arcane Deflection: At 3rd level, you have learned to weave your magic to fortify yourself against harm. When you are hit by an attack or you fail a saving throw, you can use your reaction to gain a +2 bonus to your AC against that attack or a +4 bonus to that saving throw. When you use your Arcane Deflection feature, you can cause magical energy to arc from you. Up to three creatures of your choice that you can see within 60 feet of you each take force damage equal to half your wizard level.

Fade Away: Immediately after you take damage, you can use a reaction to magically become invisible until the end of your next turn or until you attack, deal damage, or force someone to make a saving throw. Once you use this ability, you can’t do so again until you finish a short or long rest.

War Caster: You can use your reaction to make an opportunity attack to cast a spell that has a casting time of 1 action and targets only that creature.

Zargothrax has 3 legendary actions he can take at the end of a creatures turn, per round.

He uses these legendary actions to cast a single spell and use his Blink Steps feature.

Blink Steps: Immediately after you take the Attack action or the Magic action, you can teleport up to 30 feet to an unoccupied space you can see.

Power Surge: Once per turn when you deal damage to a creature or object with a wizard spell, you can spend one power surge to deal extra force damage to that target. The extra damage equals half your wizard level.