Archmage Nelkin "The Snail" Danniker

Legendary Resistance. Three times per day (or four while within his lair), if The Snail fails a saving throw, he can choose to succeed instead.

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

Divine Awareness. The Snail knows if he hears a lie.

Spellthrift: When The Snail casts a spell of 1st level or higher, he makes a spellcasting ability check with the DC = 10 + the spell's level. If he succeeds this check, the spell is cast but a spell slot is not consumed. If the check fails, the spell slot is consumed as normal. This trait cannot affect spell slots of the highest level the creature can cast if it can cast spells of multiple levels, and it also has no effect on Mystic Arcanum.

Halfling Luck. The Snail rerolls any natural 1 on a d20 roll for an attack, ability check or saving throw.

Spellcasting. The Snail is an 18th-level spellcaster. His spellcasting ability is Intelligence (spell save DC 19, +11 to hit with spell attacks). The Snail can cast disguise self and invisibility at will and has the following wizard spells prepared:

Cantrips (at will): fire bolt, light, mage hand, prestidigitation, shocking grasp

1st level (4 slots): detect magic, identify, mage armor, magic missile, shield

2nd level (3 slots): detect thoughts, excruciating deformation, mirror image, misty step

3rd level (3 slots): counterspell, fireball, fly, lightning bolt, major image 

4th level (3 slots): banishment, dimension door, fire shield, stoneskin

5th level (3 slots): cone of elements, scrying, wall of force

6th level (1 slot): disintegrate, globe of invulnerability

7th level (1 slot): teleport, forcecage,plane shift, project image, reverse gravity, symbol 

8th level (1 slot): mind blank

9th level (1 slot): meteor swarm,power word kill, time stop

*The Snail casts mind blank, fire shield and mage armor spells on itself before combat. The Snail often has a contingency spell active which casts mirror image whenever he is attacked.

Equipment. The Snail possesses several powerful magic items: Talisman of the Astral Donjon (controls the eldritch machine which imprisons the solar, allows teleportation into or out of White Plume Mountain's lower level), Crystal Skulls of the Host Tower, Quarterstaff of Warning, Wand of Parrying, Potion of Gaseous Form, 2 Potion of Healing(Superior).
The Snail has an Enduring Spellbook, with a long leather shoulder strap that threads through the book binding. The book has all his prepared spells in it, as well as the following additional spells which he doesn't have prepared:
(1st level )alarm, comprehend languages, earth tremor, fog cloud, snare, (2nd level) aganazzar's scorcher, alter self, blindness/deafness, nystul's magic aura, suggestion, (3rd level) bestow curse, blink, clairvoyance, glyph of warding, tiny servant, water breathing (4th level) arcane eye, blight, charm monster, control water, fabricate, leomund's secret chest, locate creature, stone shape (5th level) animate objects, conjure elemental, contact other plane, geas, modify memory, planar binding, skill empowerment, teleportation circle, transmute rock (6th level) arcane gate, contingency, create undead, move earth (7th level) delayed blast fireball, etherealness, mirage arcane, simulacrum (8th level) antipathy/sympathy, clone, mighty fortress (9th level) astral projection, gate, true polymorph, wish
In addition, the Enduring Spell book has several spells from before the Spell Plague, which are extremely rare finds: Alpha's Starshield, Arcane Voice, Arrow of Bone, Augmenting Wall, Coalthirst's Universal Mindbender, Cone of Elements, Excruciating Deformation.

Quarterstaff of Warning. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 13 (1d8 + 8) bludgeoning damage. 

Healing Touch (4/Day). The Snail touches another creature. The target magically regains 40 (8d8 + 5) hit points and is freed from any curse, disease, poison, blindness, or deafness.

counterspell, shield

The Snail 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. The Snail regains spent legendary actions at the start of its turn.

Teleport. The Snail magically teleports, along with any equipment it is wearing or carrying, up to 120 feet to an unoccupied space it can see.

Searing Burst (Costs 2 Actions). The Snail emits magical, divine energy. Each creature of its choice in a 10-foot radius must make a DC 17 Dexterity saving throw, taking 14 (4d6) fire damage plus 14 (4d6) radiant damage on a failed save, or half as much damage on a successful one.

Blinding Gaze (Costs 3 Actions). The Snail targets one creature it can see within 30 feet of it. If the target can see it, the target must succeed on a DC 15 Constitution saving throw or be blinded until magic such as the lesser restoration spell removes the blindness.