Going to be involved in la vl 20 one shot against Orcus and whatever else gets thrown at us and I need a good character design. I like to keep it simple so no Wizards,Sorcerers, or Warlocks. I like to be in the thick of battle with something that does a lot of dmg but can take a beating as well. I've got a Half-Orc Totem Barbarian built so far but was wondering if anyone had any better ideals. We can have a Legendary magic item, 2 other items, and then some odds and ends, Thanks

Paladin, probably Ancients if you think there is a good chance of death, or Vengeance if you don't. (Or like to do more damage)

Sword & Board, take some defensive spells. (Bless, etc) Make sure you have 20 CHA, the + to saves will change your life.

Paladin really isn't that complicated, you can get the hang of it pretty quickly. If you can handle a little more complexity maybe go 2 Warlock / 18 Paladin.

A level 20 Hill Dwarf Barbarian with 20 dex / 24 constitution and a shield would be able to tank an absolutely ridiculous amount, and because of it being a Barbarian you would also be doing some pretty decent damage. 

 I actually ended up the with a Half-Orc Totem Barbarian, unlimited rages and half dmg and everything except Psychic. Was with 2 Sorcerers and a Paladin and we kicked some major tail.

Circle of Moon druid, legendary item: ring of 3 wishes.

When you're full health with all slots use a wish to cast Simulacrum. The wish spell allows you to ignore casting time and component requiments of the spell being duplicated and so you just instantly have a second you with half your health and all of your spells and spell slots. It has all your base features too like Wild Shape.

Use bonus actions for wildshaping for near infinite HP soaking. Use your 9th level slots for either Shapechange to become dragons or Gate - the gate spell allows things like water to pass through it so you can box Orcus in and use Gate linking it to the sea of tranquility to make a waterfall of holy water. Alternatively, gate to a lava stream on the Plane of Fire and shower him with lava.

Alternatively consider shapechance into ancient brass dragon and using the Sleep Breath. If it works target is asleep for 10 minutes until woken (takes an action) or damaged. It is important to note any attack that hits but does not do damage or any spell that does not damage will not wake the target. Use Contagion / Bestow Curse to inflict lots of disadvantage and effects like Slimy Doom. Slimy Doom contagion means disadvantage on Con saves and if they take any damage they become stunned. Cast Elemental Bane: fire and then change into a Fire Elemental and simply walk through their space - resulting in them taking 1d10 fire damage, becoming stunned and they are set alight to take 1d10 at start of their turn until they use an action to put it out which, because of the constant stunning, they cannot do. Elemental Bane furrther increases damage. Your enemy is stun-locked 

Consider bestow curse or contagion to apply disadvantage to saving throws and use Feeblemind to set their Cha score to 1. Consider another curse/contagion for disadvantage to Charisma. Apply Slimy Doom contagion for stunlocking on damage and then Plane Shift them to that sea of infinite holy water mentioned before. And there is 2 of you to make these attempts and you can use the other 2 wishes also. It's therefore extremely unlikely that you cannot get this to work even against Orcus and the method is entirely 100% compliant with RAW.

My group did a Level 20 four-way Battle Royale, two rounds, and I won both with my moon druid using above tactics. First game didn't even receive a single point of damage (to my normal form, damage in wildshape was negated by wildshaping into new forms).

I hadn’t thought of the Ring of 3 Wishes, but I agree with the rest of this. A level 20 Circle of the Moon Druid is insanely difficult to kill because they’re at full HP every round as a bonus action and they have most of a druid’s Spellcasting abilities while they’re in wild shape. A 20th level druid’s Spellcasting by itself is brutal, add in unlimited HP and you’ve got a character that’s extremely difficult to stop. 

Hill Dwarf Barbarian Bear Totem With Shield Master and Tough Feats. Push your Con to 20 (Will jump to 24 at lvl 20 Barbarian) If your DM will allow Magic items Read a Manuel to push Con to 26 and you should have a nice 300+ body Tank who takes half from just about everything. 

Quote from Cyb3rM1nd >>

Circle of Moon druid, legendary item: ring of 3 wishes.

When you're full health with all slots use a wish to cast Simulacrum. The wish spell allows you to ignore casting time and component requiments of the spell being duplicated and so you just instantly have a second you with half your health and all of your spells and spell slots. It has all your base features too like Wild Shape.

Use bonus actions for wildshaping for near infinite HP soaking. Use your 9th level slots for either Shapechange to become dragons or Gate - the gate spell allows things like water to pass through it so you can box Orcus in and use Gate linking it to the sea of tranquility to make a waterfall of holy water. Alternatively, gate to a lava stream on the Plane of Fire and shower him with lava.

Alternatively consider shapechance into ancient brass dragon and using the Sleep Breath. If it works target is asleep for 10 minutes until woken (takes an action) or damaged. It is important to note any attack that hits but does not do damage or any spell that does not damage will not wake the target. Use Contagion / Bestow Curse to inflict lots of disadvantage and effects like Slimy Doom. Slimy Doom contagion means disadvantage on Con saves and if they take any damage they become stunned. Cast Elemental Bane: fire and then change into a Fire Elemental and simply walk through their space - resulting in them taking 1d10 fire damage, becoming stunned and they are set alight to take 1d10 at start of their turn until they use an action to put it out which, because of the constant stunning, they cannot do. Elemental Bane furrther increases damage. Your enemy is stun-locked 

Consider bestow curse or contagion to apply disadvantage to saving throws and use Feeblemind to set their Cha score to 1. Consider another curse/contagion for disadvantage to Charisma. Apply Slimy Doom contagion for stunlocking on damage and then Plane Shift them to that sea of infinite holy water mentioned before. And there is 2 of you to make these attempts and you can use the other 2 wishes also. It's therefore extremely unlikely that you cannot get this to work even against Orcus and the method is entirely 100% compliant with RAW.

My group did a Level 20 four-way Battle Royale, two rounds, and I won both with my moon druid using above tactics. First game didn't even receive a single point of damage (to my normal form, damage in wildshape was negated by wildshaping into new forms).

 WOW , I would not want to have to do battle with you