Taking Down a 20th Level Fighter with Goons

[AtomicPope]

All of this depends on...
* Subclass - Champions have a form of regeneration and would be just about unstoppable. Eldritch Knights cast Fireball. Only the Battle Master would run out of tricks very quickly.
* Magic Items - At 20th level a Fighter should have a magic item or two. A Sword of Life Stealing and Adamantine Fullplate would make it very difficult to kill a Champion.
* Feats - Heavy Armor Mastery would take the sting off of hordes.

 

[Yardiff]

Ok so lets build John Smith.
20, 13, 20, 10, 12, 8 Variant Human, feat Heavy Armor Mastery, 4th ASI, 6th ASI, 8th feat Tough, 12th ASI, 16 ASI, 19th (feat Shield Mastery)?

HP: 244

Champion, Dueling and Defense styles. Regain 5+con begining of each round after half hp reached. (this character should be the last to go down)

Eldritch Knight, Defense style. 20, 10, 16, 18, 12, 8. HP: 224. Sub ASI for Shield Mastery. Spells: Shield (11 rds of only crits hiting), Green Flame Blade (3d8+mod(ish) to 2 opponents plus another normal weapon attack)

Battlemaster, Defense style. Sub Martial Adept for Shield Mastery. (this character would be the first to go down)
Equipment: Adamantine Full Plate, Shield, 1d8 melee weapon.

For non-variant humans, stats will be slightly different with 4th being Heavy Armor Mastery, 19th being ASI.

At least this is my quick builds.

Edit: my mistake, Eldritch Knight only has 11 spell slot.

 

[Eltab]

If you are going to slay Boromir, plan ahead because just throwing two dozen orcs in front of him on the prairie won't do it.

- Somehow pin him in place - lure him into quicksand, say.
- Lots of archers can all take a shot at him without getting in each others' way. Place them in trees around the quicksand, and check ahead of time that they do indeed have line-of-fire.
- A few ground-pounders with very good AC and DEX, whose job is to prevent him climbing out of the quicksand; maybe equipped with a Reach weapon (so he can't melee with them or pull them in too).
- And of course the very environment is against him. Even if he destroys your soldiers, he still has to keep his armored self "swimming" AND pull himself out. If he does that while under fire, then he isn't killing off your soldiers. You did remove all the sticks and branches and roots he might use to pull himself back to solid ground, didn't you?

Note that the terrain is a needful part of the plan. You could use a pit trap, ravine, cliffside, or other place where he can't just plan 'What is my best move against these puny soldiers?'. On a flat plain or in a white room, you will need a silly-large number of soldiers, who will figure out they are just cannon-fodder - and act accordingly.