Amphibious.

Zegana can breathe air and water.

Legendary Resistance (3/Day).

If Zegana fails a saving throw, she can choose to succeed instead.

Magic Resistance.

Zegana has advantage on saving throws against spells and other magical effects.

Spellcasting.

Zegana is a 15th-level Simic spellcaster. Her spellcasting ability is Intelligence (spell save DC 18, +10 to hit with spell attacks). She has the following wizard spells prepared:

Cantrips (at will): acid splash, druidcraft, ray of frost, shape water
1st level (4 slots): color spray, expeditious retreat, fog cloud, shield
2nd level (3 slots): enlarge/reduce, gust of wind
3rd level (3 slots): counterspell, fly, slow
4th level (3 slots): control water, ice storm, polymorph
5th level (2 slots): conjure elemental, creation
6th level (1 slot): move earth, wall of ice
7th level (1 slot): prismatic spray, teleport
8th level (1 slot): control weather, dominate monster

Actions

Prime Speaker's Trident.

Melee or Ranged Weapon Attack: +10 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 12 (2d6 + 5) piercing damage, and the trident emits a thunderous boom. Each creature in a 15-foot cube originating from the prongs of the trident must make a DC 18 Constitution saving throw. On a failed save, the creature takes 9 (2d8) thunder damage and is pushed 10 feet away from Zegana. If the creature is underwater, the damage is increased to 13 (3d8). On a successful save, the creature takes half as much damage and isn't pushed.

Deluge (Recharge 4–6).

Zegana conjures a wave of water that crashes down on an area within 120 feet of her. The area can be up to 30 feet long, up to 10 feet wide, and up to 10 feet tall. Each creature in that area must make a DC 18 Dexterity saving throw. On a failed save, a creature takes 18 (4d8) bludgeoning damage and is knocked prone. On a successful save, a creature takes half as much damage and isn't knocked prone. The water spreads out across the ground, extinguishing unprotected flames it comes in contact with, and then vanishes.

Legendary Actions

Zegana 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. Zegana regains spent legendary actions at the start of its turn.

Adaptive Skin. Zegana gains resistance to one damage type of her choice-acid, fire, lightning, or thunder-until the start of her next turn.
Trident. Zegana makes one melee attack with the Prime Speaker's Trident.
Enlarge (Costs 2 Actions). Zegana casts enlarge/reduce on herself, using the enlarge option, without expending a spell slot.
Deluge (Costs 3 Actions). Zegana uses Deluge, if available.