Hi friend,
 I open this thread in search of tips to optimize a (mainly) villain of my campaign.
I left to you all the ideas that I have in hope you can confirm all of them ( I swear ).

First of all, level 17, only one rules… I can use only 2 manual ( PHB and 1 other of my choice( I’ll choice Xanathar) )

The idea is build a paladin optimized to avoid the combat frightened the enemy and distruct them when is necessary.

V. human.
Paladin 15 ( oath of conquest )
Rogue 1 ( only for take expertise on intimidation skill )
Hexblade 1 ( Hex warrior and use CHA instead STR)

Rapier and Shield  equipment

Feat:
Defensive duelist
Prodigy
ASI for boost CHA

So, few question about the mechanism and if it works as I hope.
1) Level 17 is like +6 prof, if I take the feat: Prodigy ( Xanathar ) I can double the prof.
I assume to “sacrifice” some feat in order to gain 20 CHA ( +5 ) so the Intimidation skill is like
+5(mod CHA) +[ +6(mod prof) *2(expertise)] = +17 intimidation skill.
It is good enough? Can I optimized this in every way using this 2 manual?

2) With the feat Defensive duelist is correct to have to AC:
18 (full plate) + 2 (shield) + 1 (defense: style of combat) +6 (defense duelist if it is works ) and in case ( +5 +2 Shield and Shield of Faith ) = 34 AC

Have you any other tips to optimized this character?
Other useful feat or mechanics? Equipment?
Obviously I try to avoid the STR to use all the point in CHA and CON.
The theme about the campaign is very dark so I need a character to impress the other.

Thank you so much for your help.

Tbh, I would use a dragon born instead of a V. Human, as dragon born have a racial traits of dragon's presence, which can firghten/intimidate the foe

A quick note for you, the Intimidate skill does not cause the Frightened condition. To take advantage of the the Conquest paladin, you need everything that could cause the frightened condition. Things like dragonborn fear, menacing attack from battlemaster, the fear spell, etc...

You could pick up Martial Adept to get menacing attack, forget about the rogue levels. Go Dragonborn for the fear feat. crank up your CHR and lock everybody you want down. Watch them burn in your presence. Even switch to Whip for cracking down on people at the full range of your 10' aura.

Paladin 16 gets you 4 ASIs: 2 for CHR max, Defensive Duelist, Martial Adept (Menacing Attack, +another)

Here is a nice Reddit on ways to cause frightened as well.

Unfortunately, the Dragonborn racial feat 'Dragon Fear' doen't work very well with Oath of Conquest, since the Aura of Conquest ability damages frightened enemies at the start of their turn, and Dragon Fear allows new saves to break out of the frighten effect each time the target takes damage.

Variant Human is a good choice for this character's race.  Half Elf is also an option worth considering.  There are several other good options, but they mostly require other books, and this character is stuck with PHB plus Xanathar.

To make your character as intimidating as possible, you want to:

1. max your charisma out to 20

2. get proficiency & maybe expertise in the intimidation skill.  Keep in mind that sources off expertise do not stack, so there's no extra benefit to multiclassing rogue if you already have expertisse in intimidation from the prodigy feat, or bard levels, or whatever.

3. get access spells and abilities that frighten - especially wrathful smite and fear

4. if possible find ways to reduce enemy saving throws against those effects.

5. Fear and Wrathful Smite require concentration, so you'll also want a decent constitution score, and may want to look into other ways of raising your concentration saves.

Assuming the use of point buy and the Variant Human race, you can start with at most a 16 charisma, so two of your Ability Score Improvements have to go into boosting your charisma.

7 levels of Conquest Paladin will give you Skill proficiency in intimidation,  one of the required two ability score improvements, aura of conquest to prevent frightened enemies from running away, the Wrathful Smite spell for a strong single target frighten effect using first level spell slots, and the Conquering Presence channel divinity ability, a large, party friendly frightening burst effect that doesn't require concentration and comes back on a short rest.

That leaves ten levels left to work with to pick up expertise, the Fear spell, another ability score improvement, maybe some boost to concentration saves, and maybe some ways to reduce enemy saves against your frighten effects.  You have some options here.

- the prodigy feat, which you can take as your human bonus feat can get you expertise.  Prodigy can also get you proficiency in a woodwind musical instrument, which might be relevant depending There are stronger feats to choose from, so if you can get expertise otherwise you might not want to take this.

- two more levels of paladin can get you the fear spell and another ability score improvement

- 9 levels of Arcane Trickster rogue get you expertisse, 2 ability score improvements, and magical ambush to debuff saving throws, but you can's get the Fear spell by level 17, and multiclassing rogue paladin is very hard on your stats, since you need to max out charisma, you want at least 14 constitution for concentration saves and hit points, and you need either strength 15 to move in the best heavy armor or dex 14 to make full use of medium armor.

- 6 or more levels in shadow sorcerer gives you the fear spell, at least one ability score improvement, plus the highten spell metamagic and hound of ill omen abilities that allow you so spend sorcery points to give targets disadvantage on saves against your frighten spells a couple times a day.

- 7 or more levels in divine soul sorcerer gets you the Fear spelk, an ASI, and heighten spell, just like shadow sorcerer.  You don't get hound of ill omen, but you do get access to Spirit Guardians, which is a strong concentration spell to use when confronted with enemies that are immune to frighten, and 'favored by the gods', which can help you pass important concentration saves.

- 5 or more levels of college of whispers bard gets you expertise, the Fear spell, and the words of terror ability.  Unfortunately, words of terror is a non-combat ability and mostly works to make the rarget frightened of someone other than you, because if you make them frightened of you then your aura of conquest will damage them, which ends the effect.

- 1 level of hexblade doesn't make you more intimidating, but it does let you make weapon attacks using charisma, which helps a lot.  Plus you get a whole bunch of other abilities, and a short rest spell slot to use on wrathful smite.  Hexblade multiclass is very good, but don't feel like you have to take it, as your character concept tries to rely more of intimidation rather than direct combat ability, and you will have at least a +2 weapon attack modifier from either the 15 strength you need for heavy armor or the 14 dexterity you need if you go for medium armor instead.

- 5 or more levels of hexblade gets you a bunch of great hexblade stuff plus the fear spell and two spell slots to cast it with per short rest so you'll be able to throw the spell out at least once in almost every encounter.

there's also magic items to consider.  By 17th level most characters have collected a few, but I don't know if this character gets to start with any.  If you do, there are a few general categories to consider:

basic upgrades: magic weapon, magic armor, magic shield, cloak of protection, etc.  Anything that provides a straight bonus to hit, damage, ac, saving throws, etc.  At the very least some magic weapon to bypass common damage resistance to non-magicsl wespon attacks.

frighteners:  there are three msin ones that all work similarly:  wand of fear, mace of terror, and pipes of haunting, the latter of which requires proficiency in a woodwind instrument to use.  The mace of terror can also be your magic weapon for bypassing damage reduction, but the base damage fot a mace is low and it doesn't provide bonuses to hit or damage, so even if you can get one you might still want another magic weapon to actually fight with.

Strength fixers:  gauntlets of oger power or belts of giant strength set your strength to particular high values, 19 or more depending on the item.  The 19 syrength gauntlets aren't even especially rare - many published adventures include opportunities to grab them.  Any of these will bypass the need to raise strength or multiclass hexblade.  Hexblade multiclass remains a strong option regardless, but if you don't need it to fix your weapon attack stat then you can afford to skip it if you need those levels for something else.

...

Putting it all together

...

Clearly there are several ways ooen to build this character, I'm only describing one posdible build...

or i would be if i weren't out of t8me.  Back in a bit...

ok.  Putting it all together, based on the following assumptions: 1. point buy, 2. the character starts at 17th level, so the order of abilities doesn't matter too much.  Anything that directly improves your ability to intimidate or frighten enemies will be in bold.

base stats: str 14, dex 10, con 14, int 8, wis 10, cha 15
Alignment: Lawful Evil, because of course.
race: variant human, +1 strength, +1 charisma, proficiency in perception, fluent in common and undercommon
vuman bonus feat: Prodigy, proficient in intimidation, expertise in intimidation, proficiency in pan pipes, fluent in infernal
background: Noble, knight variant.  Proficiency in persuasion and history, fluent in draconic, retainers feature

levels 1-7: Paladin 1-7
level 1: proficient in simple & martial weapons; light, medium & heavy armor, shields, insight, and athletics.  Lay on Hands, Divine Sense.
level 2: divine smite, defense style, spell casting including Wrathful Smite which you should always have prepared.
level 3: Oath of Conquest, including the Conquering Presence channel divinity which you should try use as often as possible
level 4: Ability Score Improvement: +2 Charisma
level 5: Extra Attack, second level paladin spells including Find Steed and Spiritual Weapon
level 6: Aura of Protection
level 7: Aura of Conquest

levels 8-16: Sorcerer 1-9
level 8: Sorcerous Origin: Divine Soul, Lawful type for Bless, Divine Magic for cleric spell access, Favored by the Gods, useful spells including and Shield and Absorb Elements
level 9: Sorcery Points
level 10: Metamagic, including Heighten Spell
level 11: Ability Score Improvement: +2 Charisma
level 12: third level sorcerer spells, including Fear
level 13: empowered healing
level 14: fourth level sorcerer spells including Spirit Guardians, to use when confronted with fear-immune enemies.
level 15: Ability Score Improvement: War Caster, improving your concentration saves, making spell casting easier in combat, etc.  No opportunity attack Booming Blade due to your source limits, but opportunity attack Command can be good.
level 16: fifth level sorcerer spells.

Level 17: the last level depends on the magic item situation.  If you can grab one of the strength fixing magic items, then make your last level Paladin 8, to bump up your spellcasting, hit points, and lay on hands a bit, and to grab an ability score improvement or the Lucky feat.  If you cannot grab a strength fixing item, then take a single level of hexblade for hex warrior to let you fight with charisma, along with hexblade's curse and a single first level spell slot that recharges on a short rest.

All together, you'll have a +17 to intimidate checks, potentially with re-rolls if you're able to take the lucky feat at level 17.  You've got the spellcasting slots of a 12th or 13th level spellcaster, with difficult-to-escape frighten spells in Wrathful Smite and Fear, and enough sorcery points to give at least 3 targets a day disadvantage on their initial saves via Heighten Spell.  You have a +7 with advantage on concentration saves, and can add an extra 2d4 from favored of the gods or possibly an extra roll from lucky if needed to effectively maintain your frightening spells.  You also have Conquering Presence once per short rest with a bigger, party-friendly area of effect and no concentration requirement (so you could use conquering presence then follow up with Wrathful Smite or Fear to tag enemies that pass their saves), though it is easier to escape since it allows new saves at the end of enemy turns.

When confronted with fear-immune enemies you've got a variety of other useful spells including but not limited to Shield, Absorb Elements, Bless, Spiritual Weapon, and Spirit Guardians.  You also have plain old divine smite, though your actual spell selection is good enough that smites should be saved for special occasions like critical hits against key foes.  When you are forced into combat you have an AC of at least 21, a weapon attack bonus of at least +10, and an athletics score for shoving and resisting grapples of at least +8, all possibly higher depending on magic items.  Depending on that last level you may also have Hexblade's Curse for an additional damage buff when needed.  You can wear the most imposing heavy armor, can speak a variety of scary languages including undercommon, draconic, and infernal, and are proficient in perception to help you notice when an enemy is trying to sneak past you and insight to judge when an enemy is really intimidated by you and when they're just pretending, or better yet to help pick up on what their emotional vulnerabilities might be.  You also have a re-summonable fiendish warhorse to look cool and imposing riding around on, and a handful of personal retainers to cater to your whims.

This isn't necessarily the strongest character, or even the strongest Conquest Paladin, that could be built at this level.  Prodigy, for instance, is necessary here to get the desired expertise bonus in intimidation, but a +11 is usually good enough, and that feat could be more effectively applied in combat as Sentinel, Alert, Inspiring Leader, Resilient, or some other more combat oriented feat.  If I was starting a Conqueror at 17th level, I would personally go straight paladin with no multiclassing at all, as that's only one level shy of the 18th level paladin aura expansion, and within plausible leveling distance of the fantastic 20th level Conquest capstone.  But that would mean skipping out on Heighten Spell, which is a huge deal when it comes to maximizing your ability to effectively frighten enemies at high levels, so if you really are focused on intimidation and frighten above all else, then at least some sorcerer is essential imo.  You could go with shadow sorcerer instead, that hound of ill omen is great and very on brand, but you can get more or less the same effect for the same cost out of heighten spell, and the save boost and divine spell access are more generally useful for this character than the shadow sorcerer's Darkness abilities, especially as you do not want to be spending sorcery points on anything other than debuffing enemy saves.  Besides, this is a character who wants to be seen.

Ditching rogue is unfortunate, but the stats just don't work out right due to multiclassing requirements.  That, and the only thing rogue really gets you for this concept without going a full 9 levels of arcane trickster is that expertise, and if you were going to spend whole class levels on that then bard would be a better call, for the better spell slot progression.

Again though, this is just one example of how you might build this character.  As laid out in the previous post, there are a lot of potential building blocks to choose from and a lot of ways that they could be stacked together.  And that's with the 'PHB + 1' restriction.  Without that restricion, there'd be even more to consider, and possibly more yet when Tasha's hits the shelves later this year, especially if the Undead warlock patron makes it to print in anything like the playtest form.  And speaking of playtests, if your DM was open to old Unearthed Arcana content, we'd also want to look at the Menacing feat as an alternative to Prodigy.  And if you weren't starting at level 17 but instead had to play the character up from level 1, that would also change things.  I might take that hexblade level much earlier, or else try to start with a 16 in strength.  I might take paladin to level 9 before multiclassing into sorcerer to avoid delaying access to the Fear spell, which would then change how many levels of sorcerer I was able to take at all, etc.

But I've rambled on enough for now.  I hope any of that was helpful.