What is the highest average charisma skill check a solo character can get, without directly using magic?

Question

I was building a character that had levels in Fey Wanderer Ranger, that gains Otherworldly Glamour which allows you to add wisdom to charisma checks, and then I noticed Samurai fighters get Elegant Courtier which has the same bonus.

Emboldened by the fact they stack, I started to look for other class features that, for instance let you reroll failed intimidation checks or gain advantage in some way.

It made me wonder, what is the highest possible average charisma skill check by a solo character, without casting magic spells on themselves?

This character may be up to 20th level, have Epic Boons, and have their ability scores based on the standard array.

(This means no spells, or magic items and no outside assistance except by summoned/created creatures, e.g. a familiar using the help action is ok, but a party member using flash of genius is not.).

Answer 1

A wildly lucky fey wandering samurai with a fiendish friend: 53.49 average

Our character:

• Rogue 1 for Expertise. This level is replaceable by the Prodigy or Skill Expert feats (eg. from v. Human), but to my knowledge we don't get to do anything useful with that level

• Some race which gives +2/+1 to Wisdom/Charisma in either combination

• Fey Wanderer Ranger 4 for Otherworldly Glamour adding Wisdom and an ASI

• Samurai Fighter 8 for Elegant Courtier adding Wisdom and three ASIs

• the Fiend Warlock 6 for Dark One’s Own Luck adding a d10 and an ASI

• Wild Magic Sorcerer 1 for Tides of Chaos to give ourselves advantage

• Has the Lucky feat using one of the above ASIs

• As the Boon of Luck for another d10

Starting from the standard array we assign the 15 and 14 to Charisma and Wisdom, and 13 to Dexterity for multiclassing purposes. After racial bonuses we need 4 ASIs to get Charisma and Wisdom both up to 20.

To one Charisma (Persuasion) check we then get to use Tides of Chaos for advantage and spend a Luck point so we are rolling 3d20 and taking the highest. In addition to our Charisma modifier we add bonuses equal to twice Wisdom modifier, twice our proficiency bonus and 2d10.

$$ \text{Average of highest of 3d20 } + \text{Cha mod} + 2 \times \text{Wis mod} + 2\times\text{Proficiency} + \text{Average of 2d10} = $$ $$ 15.49 + 5 + 2\times5+2\times6+11 = 53.49 $$

Answer 2

The maximum average result for a Charisma check is at least 70.99

The Character

Our character is a 20th level character from Theros, and has the following classes:

• Bard (College of Lore) 18 ------------ for (Bardic Inspiration, Expertise in Deception, Peerless Skill, Magical Secrets for wish, the Lucky feat, the Actor feat and 2 ASI to Charisma)
• Cleric (Peace Domain) 1 ------------- for (guidance and Emboldening Bond)
• Any other class 1

...has the Oracle Supernatural Gift from Mythic Odyssey of Theros:

Oracle’s Insight. The gods give you flashes of insight that help you bring your efforts to fruition. When you make an ability check, you can roll a d10 and add the number rolled to the check.

...and the following Epic Boons:

• Boon of Fate
• Boon of Luck

Finally, our character has created a simulacrum of themself with the wish spell.

The Calculation

We will be making a Charisma (Deception) check to pass off a disguise.

Our d20 roll follows:

• Advantage from the Actor feat
• A Luck Point is expended

The average of our d20 roll after these effects is 15.49

Our personal modifiers are as follows:

• Charisma score is 20 (+5 bonus)
• Expertise in Deception (+12 bonus)
• Peerless Skill adds 1d12 (average of 6.5)
• Oracle's Insight adds 1d10 (average of 5.5)
• Boon of Luck adds 1d10 (average of 5.5)

This totals an average of +38.5.

The modifiers granted by our simulacrum are as follows:

• Bardic Inspiration adds 1d12 (average of 6.5)
• guidance adds 1d4 (average of 2.5)
• Emboldening Bond adds 1d4 (average of 2.5)
• Boon of Fate adds 1d10 (average of 5.5)

This totals an average of +17.

Grand total: 70.99

Variant Rules

Two variant rules let us push this total a bit further, these being:

• Proficiency Dice
• Hero Points

Proficiency dice replaces the +12 from Expertise with +2d12 which averages to +13. Overall this nets +1

Hero Points adds 1d6 to the check for an average of +3.5

Variant Rule total: 75.49

Infinite Simulacra

Technically, there is no limit if you can continue to create simulacra of yourself. The distinction here comes from the simulacrum spell which says:

If you cast this spell again, any duplicate you created with this spell is instantly destroyed.

However, if your newly created simulacrum casts wish to make a simulacrum (Epic Boon of High Magic grants the additional 9th level spell slot) it is not you casting it, so you continue to rack up simulacra. Since they each have Boon of Fate, you could add 5.5 for every simulacrum bearing no limit.

Answer 3

Another way to get 53.49 on a Charisma (Persuasion) check, on average: A half-elf samurai fighter 8, fiend warlock 8, and redemption paladin 4, with two feats and an Epic Boon

It’s the same average as in @Someone_Evil ‘s answer, but gotten a different way.

Race

The character is a half-elf, which increases their Charisma and two other scores as well as qualifying them to take the Prodigy feat. For the Skill Versatility racial trait, one of the skills must be Charisma (Persuasion).

Classes and subclasses

These do not need to be taken in any particular order, because the skill proficiency comes from elsewhere (Skill Versatility), so I’m ordering them in order from fewest levels to most levels.

• Oath of Redemption paladin: 4 levels. This gives the Channel Divinity feature and the option Emissary of Peace, which gives +5 to Charisma (Persuasion) checks for 10 minutes, as well as an ASI.
• Samurai fighter: 8 levels. This gives 3 ASIs and the feature Elegant Courtier, which lets them add their Wisdom modifier to Charisma (Persuasion) checks.
• Fiend warlock: 8 levels. This gives 2 ASIs, a Pact Boon (the character takes the Pact of the Chain to get a familiar), and the feature Dark One’s Own Luck, which adds +1d10 (averages 5.5) to any one ability check.

Ability scores and feats

Starting from the standard array, assign 15 to Charisma, 14 to Wisdom, and 13 to Strength (for multiclassing paladin and fighter). (The other 3 scores can be allotted as you wish.) A half-elf gets +2 to Charisma, and +1 to each of two other ability scores. One of those two increases should go to Wisdom, but the other doesn’t matter. This makes the relevant ability scores 15 Wisdom and 17 Charisma.

Using 4 out of their 6 ASIs, increase Wisdom and Charisma both to 20 (modifiers of +5).

The last two ASIs they use to get the feats Prodigy (from XGtE) and Lucky. For Prodigy, choose Persuasion as the skill that gets the proficiency bonus doubled (adding +12 at 20th level).

Epic Boon

This character also gets an Epic Boon, the Boon of Luck, which allows them to add +1d10 (averaging 5.5) to any one ability check.

The check

The check this applies to must be a Charisma (Persuasion) check. Less than 10 minutes ahead of time, the character must use their Channel Divinity option Emissary of Peace. Right before the check is made, the familiar (from the warlock Pact of the Chain) must take the Help action, granting advantage on the check. The check is made, and the character chooses to use the Elegant Courtier samurai feature, the Dark One’s Own Luck warlock feature, and the Boon of Luck.

Overall, this gives:

15.49 (the highest of 3d20) + 5 (Charisma modifier) + 5 (Wisdom modifier) + 5 (Channel Divinity) + 12 (double proficiency bonus from Prodigy) + 5.5 (average of 1d10 from Dark One’s Own Luck) + 5.5 (average of 1d10 from Boon of Luck) = 53.49 on average.