What is the lowest possible level that a PC get an AC of 39 without any magic items and with help from only one ally?

Question

What is the lowest level AC a Player Character can have an AC of 39 (so a Tarrasque can't hit them without a critical hit) with help from at most one same-level ally?

No magic items may be used that the characters don't create themselves (like from Artificer or Forge Cleric for example), but all official class features, races, feats, multi-classing, and abilities are on the table.

The second character must be the same level as you.

You are also allowed to prepare beforehand, and you get as much time as necessary, so long as the characters won't die from old age.

If a certain roll has to be made (like for a Defensive Duelist), assume you roll the average roll every single time.

Show me a sustainable 3-5 round combat version.

Also don't include cover.

Answer 1

6th

A 3rd level Warforged Fighter (Battle Master)/3rd level Sorcerer (Divine Soul) can reach 39 AC with the following factors:

• 18 (Plate armor) [total so far]
• +2 (Shield) [20]
• +1 (Integrated Protection) [21]
• +1 (Defense Fighting Style) [22]
• +4.5 (Bait and Switch Maneuver) [26.5]
• +5 (shield) [31.5]
• +2 (shield of faith) [33.5]

...and the support of a 5th level Sorcerer (Divine Soul)/1st level Cleric (Forge):

• +2 (ceremony) [35.5]
• +1 (warding bond) [36.5]
• +2 (haste) [38.5]
• +1 (Blessing of the Forge) [39.5]

Answer 2

7th

Standard array assumed (not that it matters providing the tank has 16 Cha and 10 Dex and both meet multi class requirements)

Tank: Warforged Forge Domain Cleric 1/College of Swords Bard 4/Divine Soul Sorcerer 1

• Plate Mail: 18 (Prof. from Forge Domain)

• Shield: +2 (Prof. from Forge Domain)

• Integrated Protection: +1 (From Warforged)

• Blessing of the Forge (armor): +1 (From Forge Domain Cleric)

• Shield (5x): +5 (From Sorcerer, 5 spell slots of 11 available). Requires the tank is not surprised when attacked in the first round - this is a given against the Tarrasque (on average rolls) due to Jack of all Trades providing we have at least 10 Dex.

• Shield of Faith: +2 (From Divine Soul Sorcerer, 1 spell slot, Concentration)

• Blade Flourish - Defensive Flourish (3x at 16 Cha): +3.5 (d8) (From College of Swords Bard). We assume the tank targets the support to guarantee a hit (on average rolls) and the support will pass their Concentration checks (on average rolls). Since the tank will win initiative (see above) this can be activated before the tank can be targeted.

• Fighting Initiate feat - defence: +1 (From Bard 4 ASI)

Support: Divine Soul Sorcerer 5/Artificer 2

• Haste: +2 (From Sorcerer 1 3rd level slot, Concentration)
• Warding Bond: +1 (From Sorcerer 1 1st level slot)
• Ceremony: +2 (From Sorcerer 1st level slot)
• Infusion (shield): +1 (From Artificer)

Note: Apart from being a handy target to ensure hits for Blade Flourish, the Support character doesn’t need to be there, all their active involvement can be pre combat.