The Highest Unarmored AC is 76 (81 with three-quarters cover)

• Permanent AC: 36
• AC with Temporary Modifiers: 58
• One-attack AC: 76 (81 max)

Permanent AC with no Magic Items: 12

• Abilities: 14/12/12/16/8/16 (Half-Elf applied to Strength/Intelligence)
• Artificer 4 [for 1 ASI applied to Strength]
• Barbarian 1 [for Unarmored Defense]

12: Unarmored Defense

Increasing Ability Scores

• Wizard 1 [for wizard spell list]

Firstly, we will increase our Charisma via the dark gift of Zantras, described in this adventure module (spoilers):

[Curse of Strahd: Chapter 13]

South Sarcophagus. The vestige within this sarcophagus offers the dark gift of Zantras, the Kingmaker. Zantras’s gift is power that comes from great presence and force of personality. This dark gift increases the beneficiary’s Charisma by 4, up to a maximum of 22.

In order to get the other ability scores we need, we are going to use the deck of many things which includes the Star card:

Increase one of your ability scores by 2. The score can exceed 20 but can't exceed 24.

We will use time travel to kill any version of ourselves that draws The Void before the Star card until we draw 6 Stars (see the Time Travel Procedure addendum for details), increasing out Intelligence and Charisma to 24 each.

Finally, we will read a Tome of Clear Thought, and Tome of Leadership and Influence resulting in:

• Abilities: 14/12/12/26/8/26

Adding Magic Items and Other Rewards: 36

• Artificer 14 [for Magic Item Savant, and the Dual Wielder feat]

+8: one of the chromatic dragon masks (+Charisma modifier)
+4: Sword of Kas having activated the +3 AC and with the 91-00 Minor Beneficial Property
+4: Wand of Orcus with the 91-00 Minor Beneficial Property
+3: A defender having activated the +3 AC
+3: A moonblade with three 01-40 runes and an 85-86 rune having activated the +3 AC
+1: Dual Wielder (also grants +1 attack)
+1: Blessing of Protection

We will be able to hold all 4 weapons, and attack with the Sword of Kas, defender, and moonblade because of the next section.

Adding Temporary Effects and Spells: 58

• Wizard (Bladesinger) 2 [for Bladesong]

+12: Unarmored Defense improvement via a scroll of shapechange assuming the form of Yan-C-Bin (Dexterity and Constitution modifiers from +1 to +7)
+8: Bladesong (+Intelligence modifier)
+2: Potion of Speed (also grants +1 attack)

Once Yan-C-Bin, use Change Shape to polymorph into a four-armed humanoid such as a thri-kreen.

Expected AC for One Attack: 71 (min), 76 (avg), 81 (max)

• has Artificer (Alchemist) 14 [for Experimental Elixir and the Martial Adept feat for Evasive Footwork]
• has Wizard 1 [for shield]
• Bard (College of Swords) 3 [for Bardic Inspiration, and Blade Flourish]

+5: 3/4 cover
+5: shield
+1: Experimental Elixir: Resilience
+1d6: Defensive Flourish
+1d6: Evasive Footwork

Summary of Classes and Gear

For summary sake, these are the final class requirements:

• Artificer (Alchemist) 14 [for Experimental Elixir, 1 ASI, the Dual Wielder feat, the Martial Adept feat, and Magic Item Savant]
• Bard (College of Swords) 3 [for Bardic Inspiration, and Blade Flourish]
• Wizard (Bladesinger) 2 [for shield, the wizard spell list, and Bladesong]
• Barbarian 1 [for Unarmored Defense]

...and these are the final gear requirements:

• many Legendary spell scrolls including shapechange, true polymorph, and wish
• a deck of many things
• a Tome of Clear Thought
• a Tome of Leadership and Influence
• a chromatic dragon mask
• the Sword of Kas
• the Wand of Orcus
• a defender
• a moonblade
• a potion of speed
• an Experimental Elixir of Resilience

Dragonmark

Our character can get 2 more AC if he is able to become a Bladesinger without being a half-elf:

Only elves and half-elves can choose the bladesinger arcane tradition. In the world of Faerûn, elves closely guard the secrets of bladesinging.

Your DM can lift this restriction to better suit the campaign. The restriction reflects the story of bladesingers in the Forgotten Realms, but it might not apply to your DM’s setting or your DM’s version of the Realms.

If, instead, our character can choose the Bladesinging Arcane Tradition in Eberron, our choice of race can switch to a human with the Mark of Sentinel Dragonmark. This gives access to the shield of faith spell which can be placed into a Spell Glyph via glyph of warding for +2 AC.

With this, you would apply the Ability Scores as follows (after racial bonuses): 13/12/10/15/9/15, and use the level 4 Artificer ASI for +1 Intelligence and +1 Charisma (applying the Star cards as normal).

Time Travel Procedure

• Be ready to use a scroll of true polymorph to assume the form of a gynosphinx in a sphinx lair you have claimed for:

The flow of time within the lair is altered such that everything within moves up to 10 years forward or backward (sphinx’s choice).

• Go forward in time 10 years; if the ground is marked in a specific way (see later), go back in time and proceed, otherwise go back in time, and kill yourself before you draw and wait until you can go back in time and proceed.
• If you get to proceed, prepare to begin drawing from the deck of many things by using a scroll of wish to replicate the effect of clone.
• Then draw 1 card from the deck of many things repeatedly until you draw the Star.
• Mark the ground to indicate to your past self (who has one less Star card drawn) that you drew the Star card before The Void.
• If you are killed, you will wake up as a clone. Proceed as normal including using a new scroll of clone.

Repeat the second phase until you have drawn 6 Star cards.

To further illuminate the results of this procedure, here is a description of what takes place:

• The earliest version of yourself will go forward in time to check for a mark indicating he will be successful if he goes back and begins right away. Otherwise, it will indicate that he will draw The Void before Star.
• In this case, the correct option is to kill that version to delay the drawing. This new version who is delayed will again go forward in time to check for a mark (possibly coming back to kill the version who just killed its pre-clone).
• Eventually, the mark will be there so that you know to go back and immediately proceed (at this point there will be no one to kill since everyone else is either dead, or in the next starting point detailed below).
• Every time you get a Star card, you lock that in by creating a new starting point at that point in time.
• Then you just repeat until you've 6 Star cards; on average this takes somewhat more than 30 minutes.

(assuming that drawing 1 card takes 1 turn and killing yourself takes 1 minute; it is somewhat more because you will also have to fight some avatars of death).

• Over the course of the drawing you will also become bankrupt of everything except magic items and accrue a number of powerful fiends and NPCs as enemies (which you can use scrolls of wish or wishes granted by the Moon card to abate).

Note: This does fall into the Grandfather Paradox in some ways; However, most resolutions to the Grandfather Paradox allow this system to work:

• If time resists paradoxes by being self-consistent, the simplest thing is that every time you go to draw you happen to draw Star before The Void because otherwise the paradox kicks in. Essentially, world states where you draw The Void first are impossible, since that version of yourself would never have the chance to draw The Void first as it would already be dead.
• That being said, resolving time paradoxes is entirely within the purview of the GM. If these paradoxes make increasing your ability scores in this way impossible, then your AC will not be as high unless you draw 6 Star cards before The Void which has a chance of around 1.5%.