Bane of Cronus. Zeus has spent millennia fighting a god of time. Whenever Zeus is affected by chronurgy or time magic, he can make a Wisdom save equal to 8 + proficiency + spell casting modifier. On a success, he is immune to the effect.

Divine Weapons. Zeus's weapon attacks are magical. When Zeus hits with any weapon, the weapon deals an extra 144 (12d12) lightning or thunder damage (included in the weapon attacks below).

Divine Thunder. Zeus's lightning and thunder damage is maximized. Furthermore, he deals double damage to Aberrations, Celestials, Fiends, Monstrosities, Structures, and Undead. 

Godly Constitution. Zeus's hit dice are maximized.

Godly Power. Zeus's attacks treat immunities as resistance, and invulnerability as independent structures with 1,000 hit points (autohit, autofail).

Legendary Resistance (3/day). If Zeus fails a saving throw, he can choose to succeed instead.

Legendary Ability (3/day). If Zeus fails something that would require a roll, he can choose to succeed instead.

Lucky (10/day). Zeus has 10 uses of the lucky feat, of which he can use multiple at once.

Magic Resistance. Zeus has advantage on saving throws against spells and other magical effects

Master Bolt. Zeus's symbol of power, a lightning bolt, is a +3 magical weapon. It has 100 charges. 

When Zeus scores a weapon attack, he can choose to expend a charge to deal an extra 8 (1d8) damage (lightning or thunder), to a maximum of 80 (10d8)

While holding the weapon, he can expend some of its charges to cast one of the following spells, which deal lightning or thunder damage, from it (spell save DC 30, +22 to hit with spell attacks): Counterspell (7 charges), Conjure Elemental (7 charges), Dispel Magic (3 charges), Fireball (7th-level version, 7 charges), flaming Sphere (2 charges), Ice Storm (4 charges), Invisibility (2 charges), Lightning Bolt (7th-level version, 7 charges), Passwall (5 charges), Plane Shift (7 charges), Telekinesis (5 charges), Wall of Fire (4 charges), or web (2 charges).

Wrath of Olympus (Recharges after a Short or Long Rest). If Zeus would die, he is now gargantuan, his current hit point total instead resets to ten times his hit point maximum, he no longer needs to recharge his Lightning Bolts nor Thunder Bolt ability, his ability scores are increased by 10, he gains 5 uses of Legendary Resistance, and he gains 3 uses of Legendary Ability. Furthermore, Zeus is immune to all conditions and can now use the options in the "Mythic Actions" section for 1 hour. Lastly, the rest of the current turn is skipped and Zeus takes one turn immediately after.

Wrath of Zeus. When Zeus's Wrath of Olympus trait is activated, when one creature does more than 600 damage to him in one round, when he takes more than 1,200 damage in one round, or when he drops to 0 hit points, he cannot be targeted nor take any damage until the start of his next turn. On his next turn, all creatures within 50 feet of Zeus take 504 (42d12) lighting or thunder damage. All creatures within 150 feet of Zeus take 252 (21d12) lightning or thunder damage.

Multiattack. Zeus can use his tyrannical presence. He then makes two Blade of Olympus or Lightning Bolts attacks and makes one use of Thunder Bolt.

Blade of Olympus. Melee Weapon Attack: +22 to hit, reach 10 ft., one target. Hit: 23 (2d12 + 10) force damage plus 144 (12d12) lightning or thunder damage.

Lightning Bolts (Recharge 4-6). Ranged Weapon Attack: +22 to hit, range 600 ft., eight blasts. Hit: 22 (1d12 + 10) lightning damage.

Thunder Bolt (Recharge 4-6). Ranged Spell Attack: DC 30 Dexterity saving throw, range 300 ft., radius 40 ft. Hit: 94 (24d6 + 10) force damage plus 154 (24d6 + 10) thunder damage. Success: Half damage.

Tyrannical Presence. Each creature within 300 feet of Zeus must make a DC 30 Wisdom saving throw or do one of the following things on their next turn:

Bolt. Zeus doubles his movement speed.

Counterspell. Zeus casts counterspell.

Zeus can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. Zeus regains spent legendary actions at the start of his turn.

Attack. Zeus moves up to half his movement speed and makes one Blade of Olympus or Lightning Bolts attack.

If Zeus's Wrath of Olympus trait has been activated in the last hour, he can use the options below in place of Thunderbolt.

Master Bolt (Recharge 5–6). Ranged Spell Attack: +22 to hit, range 300 ft., radius 20 ft. Hit: 360 (60d6) lightning or thunder damage.

Tornado (Recharge 5-6). Zeus creates a 20-foot-radius cylinder of destructive wind centered on a line within 600 feet of himself. For ten minutes, the cylinder and any space within 300 feet of it are difficult terrain, and nonmagical objects fully inside the sphere are destroyed if they aren’t being worn or carried. When the cylinder appears and at the start of each of Zeus's turns until the spell ends, unsecured objects within 300 feet of the sphere are pulled toward the cylinder's center, ending in an unoccupied space as close to the center as possible. A creature that starts its turn within 300 feet of the cylinder must succeed on a DC 30 Strength saving throw or be pulled 100 feet toward the cylinder's center, ending in an unoccupied space as close to the center as possible. A creature that enters the cylinder for the first time on a turn or starts its turn there takes 28 (5d10) force damage and 50 (5d10) lightning damage and is restrained until it is no longer in the sphere. A creature can use its action to make a DC 30 Strength check, ending the restrained condition on itself or another creature in the cylinder that it can reach. Zeus is immune to this feature.

Conjure Lesser Diety (Recharge 6). Zeus summons a lesser god or creature/PC with a CR of less than 21 in an unoccupied space within 300 feet of him.

If Zeus's Wrath of Olympus trait has been activated in the last hour, he can use the options below as bonus actions.

Teleport. Zeus makes a Lightning Bolts attack and teleports to an unoccupied space within 10 feet of one of the targeted creatures.

If Zeus's Wrath of Olympus trait has been activated in the last hour, he can use the options below as legendary actions.

Lightning (Costs 2 Actions). Zeus attempts to recharge all three of his rechargeable abilities and can use one of them, if available.