I just found out I’ll be playing in a level 20 one shot

[Klorox]

I’ve never played a character above level 11. Now what do I do?

There will be three characters. I am pretty sure one is playing a single classed barbarian.

I usually like playing spellcasters. I’m thinking a level 20 moon druid would be spectacular, but part of me wants to try a level 2 paladin/18 sorcerer.

What other ideas are great for level 20? I’m very willing to try something weird or different. I just want interesting.

We will have very little gear to start off.

[Crgaston]

Do you know what your stats will be?

An epic array might open up some unusual combos.

A Paladruid might be fun, and somewhat unusual. PAM+Shillelagh for multiple smites per round.

[CTurbo]

20 level Paladin. Any Oath. Pretty much all the capstones are great. Conquest or Oathbreaker especially.

[Solunaris]

If you want to try the Paladin 2 Sorcerer 18 combo, might I suggest going Warlock Hexblade 1 instead of Sorcerer 18?

Getting the Curse off to double your crit chance and allowing for Cha to be used for attacks instead of Dex is great. This way you can start as Sorcerer to get Con save proficiency and use Paladin multiclass to get Medium armor proficiency and shield proficiency for AC. This way you only need a Dex of 14 and a Str of 13 for the multiclass. If you are using a point buy this would allow you to start as a Half-Elf to get amazing Con, Cha, and decent Wis whil still giving you room for a few feats.

[Waazraath]

I'd go for something with a great capstone; simply cause most people have few opportunities to ever use it. So yeah, paladin 20 or moon druid 20 seem great.

[Citan]

I’ve never played a character above level 11. Now what do I do?

There will be three characters. I am pretty sure one is playing a single classed barbarian.

I usually like playing spellcasters. I’m thinking a level 20 moon druid would be spectacular, but part of me wants to try a level 2 paladin/18 sorcerer.

What other ideas are great for level 20? I’m very willing to try something weird or different. I just want interesting.

We will have very little gear to start off.
There are MANY, TOO MANY great builds for level 20 characters.
So I'll just suggest single-classes by order of personal preferences of what I played or would like to play.
0. Druid (Moon first, Shepherd second): if you want to ideal mix of awesomeness, versatility and fun, look no further.
The thing is though, apart from the "hey you can't kill me I'll just wild shape again and again" and exclusive high-level spells, there is nothing particular, as in, you'll probably get the same kind of feeling you would as a level 10/12 Druid.
That why I put it at 0: it's overall the possibly best choice, but I'd actually rather advice other classes because some others are harder to build up or provide more distinctive difference in how they play at higher level compared to lower level.
Especially since you play casters: it may be a golden chance to help you love more less magical and more martial classes. :)

1. Monk: Open Hand specifically (only) for trying Quivering Palm cheeses, otherwise 4e all the way.
You skip all the painful part of getting a Monk above level 10 and you directly go to the "big awesome" section: Empty Body, Fly, Fireball|Cone of Cold and Wall of Stone|Fire will be your daily tools to waste enemies. Go Half-Elf, stack Prodigy (Expertise in Athletics) and Elven Accuracy and have fun in so many different ways... ^^

2. Paladin: any Oath really, although I'd fancy Ancients particularly: you have enough slots to have fun with Divine Smite, you know great spells (Banishing Smite, Circle of Power), and you provide very powerful support auras to the group. Plus nasty capstones (love Ancients for regen + disadvnatage against your spells).

3. Warlock: kind of like Monk, you skip the hard and sometimes frustrating part of working with limited fuel. With 4*5 slots per short rest, plus quick full refuel once per long rest, you have resources to have fun with.

4. Sorcerer: you avoid the dreaded spell & metamagic choicer conundrum.

5. Barbarian: unlimited rages? 5 ASI from the get go to specialize in damage? 24 STR and CON? If you rarely play martials, this may be the way to get you hooked (less versatile than aforementioned Monk, but also easier to play, more straightforward, especially Bear totem).

[DivisibleByZero]

Thief rogue or champion fighter, because then you can show people that they aren't anywhere near as bad as people seem to think.

[Klorox]

Do you know what your stats will be?

An epic array might open up some unusual combos.

A Paladruid might be fun, and somewhat unusual. PAM+Shillelagh for multiple smites per round.

Standard 27 point buy.

[CTurbo]

A good old fashioned level 20 Half-Orc Greataxe GWF GWM Champion Fighter would be a blast to play in a one shot.

A 20 level Tempest Cleric would be awesome, or Storm/Draconic(Lightning) Sorcerer 5/Tempest Cleric 15

Thief or Scout Rogue 20 would be great as their level 17 abilities are really good.

There are a variety of Archer builds that would be crazy at level 20.

-Fighter 2(Archery)/Valor Bard 18 with Sharpshooter/Xbow expert and choose all the best Ranger Arrow spells via Magical Secrets like Swift Quiver, Lightning Arrow, Conjure Volley, Hail of Thorns, etc...

-Ranger Hunter 5(Archery)/Rogue 15(Scout maybe)

-Ranger Gloom Stalker 5/Rogue Assassin 15

[Specter]

I've been meaning to try Monk 14/Paladin 6, just to never fail a saving throw again. Plus, Divine Fist!

[Klorox]

I've been meaning to try Monk 14/Paladin 6, just to never fail a saving throw again. Plus, Divine Fist!

I had thought about that. Even going yuan-ti pureblood to really never fail a save. LOL

[djreynolds]

I’ve never played a character above level 11. Now what do I do?

There will be three characters. I am pretty sure one is playing a single classed barbarian.

I usually like playing spellcasters. I’m thinking a level 20 moon druid would be spectacular, but part of me wants to try a level 2 paladin/18 sorcerer.

What other ideas are great for level 20? I’m very willing to try something weird or different. I just want interesting.

We will have very little gear to start off.

Paladin 6/ sorcerer 14 could be cool....... +5 to saves might help out

[LordNibbler]

How about a half-elf Paladin of Vengeance 6/Hexblade 14 with Elven Accuracy: gets a fighting style, Divine Smite, Aura of Protection, Hex Warrior, Armor of Hexes, Lifedrinker, and Master of Hexes to name a few of the highlights. It gets fewer spell slots for smiting than the sorcadin but the other features make up for it.

[Fire Tarrasque]

You could always go 20 Champion Fighter. 20-17 crits and up to 8 attacks per turn are just FUN. So is combat regen.

[KRSW]

I would say fighter as well, that just sounds super fun and is one of the best capstones. Eldritch Knight could be awesome if you have really high rolls for stats so your spell DC is good plus giving someone disadvantage on a hold person with eldritch strike can end an important encounter pretty quickly.