If the highest and most expert of each Dungeons & Dragons character class were forced somehow to stay in an arena to fight, who do you think would win and why? What would be the game plan?
I would bet on the circle of the moon druid at 20th level. They would stay in wild shape the entire fight. The druid would have an unlimited hit point pool basically. Having the capability to change shapes every turn and all day would be too much for another character to deal with. It would very difficult to say the least for an enemy to even begin to whittle down the druid's actual hit points.
Depends on the arena, and how much prep time they had for each other.
Level 20 characters with no advance warning on what they'd face, generic (If powerful) rather than foe specialized equipment, and a featureless arena that won't give advantage to high mobility/stealth: Moon Druid followed by barbarian would be my assumptions for first and second place.
With advance warning: Wizard, then Onion druid.
Here's how Wizard takes the field with advance warning. Readied Moonbeam set to go off just after the moon druid's turn, followed by power word kill. Unless exceptionally lucky or exceptionally healthy, the onion druid gets one chance to hit the wizard before being forced back into normal form and keeling over dead, or two if he wins initiative.
Edited: daishain on 9th Jan, 2018 - 4:56am
If we are talking about 20th level characters, what about a wizard with misty step or expeditious retreat as their signature spells (Cast for free, unlimited) Both are bonus action moves, one is a dash the other a teleport. Either one moves the character for free. Considering the Wiz gets unlimited use of any 1st or 2nd they choose(Prepared), that's pretty damn good.
Moonbeam is a Druid (Or Light Oath Paladin) only spell, [By The Way].
Or a Vengence Paladin As 20th level Avenging Angel, constantly forcing disadvantaged saves on a Vowed enemy.
No matter how you slice it, a 20th level anything is pretty tough. A single failed save by any character is almost guaranteed to give them a loss.
Moonbeam can be cast with a Wish spell so any class that has access to wish has access to it. With 10 minutes of prep any class with true polymorph has a real edge because they can start as a CR 20 dragon at the beginning of the fight and pick up some legendary resistances. I think those two things together are only offered to Wizards and Bards.
There are many variables here that aren't known such as having magic weapons, what their armor is like and things like that. I don't know that this can be easily answered but if any fighting class has something associated with speed and the ability to cause a lot of damage quickly then they could just go around each character killing all of them before they could know what happened. Maybe a barbarian or rogue with such items could do the job. Unless someone could instantly cast sleep on everyone.
The preparation time is one of the issues in this type of contest. I don't think that ten minutes preparation time being allowed is fair. It is a huge benefit to spell casters while it does nothing for martial characters. It would tilt the playing field too far to be a fair contest.