Face off against an exact “evil” duplicate of your current character. The initiative is yours, you may use all your current available gear, and you may prepare your spell list (if applicable) before the duel. However, you also have to control the duplicate, and on the duplicate's turn you should be trying just as hard to win as on your own. If you have some killer combo, the duplicate knows it, and if you know how to defend against that combo, well so does...you. 

Now, either tell us how the fight went (who won? highlights?) or even give us a round by round account. Hopefully you all find this fun (I mean who doesn’t want to kick their own butt?) and informative (Can you find and exploit any holes in your own defense?). P.S. If you have Counterspell, you know...have fun with that.

3...2...1...GO!

my current character is an anti-mage caster so it would basically be like 

1:i cast x 

2:no you dont your hexed now 

1:oh no i counterspell your hex now your hexed 

2:ugh okay,i cast x 

(repeat until we run out of counterspell spell slots)

1:cast x 

2:ut oh (dies)

or 

2:i cast x 

1:ut oh (dies)

Let's go with my broken 20th level AM sorcerer.

Turn 1: Psychic scream, DC 25: Autofail. Eris is now permanently stunned.

Ok, let's see, my Druid first:

1. As a BA Nishi casts Guardian of Nature - Great Tree, Action shoot arrow with (custom) shortbow (with advantage because of GoN) rolled a 14 to hit on chara sheet, Nishi's AC is 13 so it hits = 11 damage, duplicate is now down to 43 HP

2.  the Duplicate also casts GoN and uses it's shortbow, rolls 24 to hit, 10 damage, Nishi is down to 44 HP

1. Nishi rushes to the duplicate, casts Primal Savagery and slashes with his claws,  rolls 13 and only scratches the duplicate's armor

2. The duplicate casts Poison Spray on Nishi, against which he saves by rolling a 15 (so glad that the duplicate has as much luck with this spell as I when I play Nishi XDD)

1. Nishi casts Moonbeam on the duplicate.

2. The duplicate rolls a 19 and only takes 3 damage (2d10 halved), (now at 40 HP) it then BA casts Misty Step to get away from Nishi and the Moonbeam and then shoots an arrow at him. It only rolls an 11 to hit (still with adv) and the arrow bounces off of Nishi's armor.

1. Nishi casts Tidal Wave on the duplicate, against which it does not save and it takes 26 points of damage (down to 14 HP) and is prone. At the end of his turn, Nishi uses his BA to move his Moonbeam over the prone duplicate.

2. The duplicate fails it's CON save and takes 8 radiant damage from the Moonbeam (down to 6 HP), it uses half it's movement to get up and casts Cure Wounds at 2nd level on itself to gain 10 HP (now at 16 HP)

1. Nishi shoots another arrow and rolls 21 to hit (also still with adv) and does 10 damage, so the duplicate is back to 6HP

2. The duplicated saves against the Moonbeam and only takes 2 damage (down to 4 HP), it casts Cure Wounds at 3rd level and gains 24 HP (now at 28 HP) then moves away from the Moonbeam.

1.  Nishi casts Ice Knife at 3rd level, he doesn't hit,m but the duplicate still takes 17 Cold damage (down to 11 HP) then he uses his BA again to move his Moonbeam over the duplicate.

2. The duplicate saves against the Moonbeam and takes 9 damage (down to 2 HP) it then casts Dispel Magic on the Moonbeam, making it vanish and then tries to run away.

1. Nishi aims his shortbow, shoots  and rolls a 17 to hit, the duplicate takes 8 damage and is dead.

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Some notes:

• I can't wait till I finally get to use Tidal Wave in our campaign (so far my party members were always too close, or we were in a room with no space for the water)
• I completely forgot that GoN also gives advantage to CON saves so I rolled those for both without >.<
• Circle of the Land Druids hit hard >D

It would rapidly devolve into two whale-gnomes trying to out-smash each other

Thoruk 1: Rage, attack

Thoruk 2: takes huge damage, rage, attack

Thoruk 1: Takes half damage, attack

Thoruk 1 wins, because Thoruk 2  didn't rage before getting hit. And because Thoruk 2 is probably a Duck.

Alternatively, they might survive beyond the extent of their rages, and so it would come down to pure luck. Thoruk 1 has the advantage though, of potentially landing a hit on turn 1 before Thoruk 2 rages and gains resistance.

Okay, I'll do my first level Goliath Sorcerer.

Kralog 1: Casts magic missile on Kralog 2, dealing 12 damage. 

Kralog 2: Uses Stone's Endurance reaction to reduce the damage by 5. Then casts magic missile on Kralog 1 for 6 damage.

Kralog 1: Uses Stone's Endurance reaction to reduce damage by 11 (to 0). Then casts magic missile on Kralog 2, killing him.

my other current character would probally just not fight and just play around maybe play a game of chess.

It would immediately fall into a "Who can hold witch bolt the longest?" contest.

My first level warlock, Praeda.

P1 initiative: 4

P2 initiative: 12

Winner casts sleep. 26

P1: hex, dagger. Attack: 10 Damage: 12 Miss.

Round two: Attack: 21 Damage: 9

P2 is awake, dagger: Attack: 25 Damage: 6

P1 again: Attack: 23 Damage: 7

P2 dies, P1 wins.

With my rogue it's all going to come down to rng. Whoever wins initiative is probably going to win, unless they get bad rolls. My DM allows me to use the careful aim optional class feature on my rogue so it'd probably come down to them sniping at eachother using the advantage from aim to get sneak attack damage. 

Alternatively, they'd try to hide if they can and then use spell ambush to impose disadvantage with hold person on the other to try and go for the auto crit. Our WIS saves aren't great so whoever goes first could potentially lock the other down and a single sneak attack crit is likely to 1 shot us. 

So with either approach it's basically down to luck. Whoever wins initiative is probalby going to win. 

Edit: Decided to play this out. Assuming a wide open field with nowhere to hide to make this easier for me to simulate. 

Evil Twin wins initiative with a 23 over my 21. 

Eveil twin uses aim and attacks with her crossbow with advantage. Attack roll is 29.  Deals 21 damage. I uncanny dodge to reduce it to 10 damage. 

My turn. Aim and attack with crossbow. Attack roll is 27. 32 damage, but Evil Twin uncanny dodges it to 16. 

Evil twin attacks. 26. Deals 21 damage again which I then uncany dodge to 10 again. 

My turn. 32 attack roll.  22 damage, uncanny dodge to 11. 

EVIL TWIN CRITS. 44 damage I uncanny dodge to 22. 

My turn: 27. 33 damage which cuts down to 16 after uncanny dodge. 

Evil twin attack roll is 28. 30 damage. I'm down. 

Maybe I'll play out one with them fishing for hold person casts instead later, but as is my evil twin came out victorious with just 10 hp left. 

Since I play a rogue, I can deal FAR more damage in one round than I can take, so... provided I make that first hit count? Jack can take out his evil double. But if he biffs that first roll, then he will... well, probably try running away tbh.

We would probably be dueling for a long while because i'm a dragonborn barbain, but for some reason i wear chainmail armour which means i have a decently good ap (16 ap, i have kinda bad dexterity and decent consititution so its worth it to wear armour instead of using unarmoured defense). My character is also pretty chaotic so we might not have gotten into a fight and instead just burnt a village down to settle our differences.

Ooooh 'the initiative is ours.' If I guarantee my rogue going first she'd most likely destroy the evil one. The battle would mostly be them using their longbow to steady aim shoot at eachother. Outside of some rng shenaigans like the evil one getting more drits/the good me somehow missing etc (not likely with a +13 to hit against 17 ac with advantage), it'd be fairly easy to take out the evil clone. 

Assuming a straight up fight to the death in an open field. If there were places to hide, the evil rogue could potentially get away. I have a far higher stealth than perception modifier so if it turned into a duel in the shadows it wouldn't go anywhere until someone eventually rolls a really good perception and a terrible...actually hold on. 

I have +15 stealth with reliable talent at play, meaning I cannot roll below 25 stealth and my max is 35. My perception is +6, so a range of 16 to 26. The stealth game would quickly devolve into us waiting for someone to get a nat 20 on perception to find the other one hiding so at that point it's really anyone's game. 

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My level 6 silver dragonbloodline sorcerer would be potentially more interesting. Their metamgics are twinned spell and trandmuted spell. But I think initiative would give the real one the edge over the evil one. She could get in that first hit with a cold spell and deal the extra damage, then can use elemental affinity to get resistance to cold damage. Forcing the evil one to either attack with cold damage against resistance in order to make herself resistant, or forcing her to use fire damage without the bonuses from her elemental adept feat or elemental affinity class feature. If the evil clone doesn't use a cold spell (or transmute a spell TO cold) then she forgoes another turn without resistance, allowing the real me to keep doing full damage. If she does use cold, then she's dealing half damage. I think she'd have to try for best of both worlds with ice knife, to get her own cold resistance up and deal some piercing damage at least that won't be mitigated. 

This would allow the real me to say, open with fireball transuted to cold and then it would be ice knives back and forth until one of us dies. We only have 14 DEX so an AC of 15 for both of us and only +2 to dex saves against spell save 15 and spell attacks +7. So while misses/successful saves are possible, they are less likely than failed saves/hits. 

So unless rng throws a curveball, there's not much of a clever strategy the evil clone can pull to win. 

Quote from CatDetective >>

Since I play a rogue, I can deal FAR more damage in one round than I can take, so... provided I make that first hit count? Jack can take out his evil double. But if he biffs that first roll, then he will... well, probably try running away tbh.

How do you sneak attack yourself, and wouldn't the other you be trying to sneak attack you too?    I see rogue vs. mirror rogue likely just running away from each other.

Quote from MidnightPlat >>

Quote from CatDetective >>

Since I play a rogue, I can deal FAR more damage in one round than I can take, so... provided I make that first hit count? Jack can take out his evil double. But if he biffs that first roll, then he will... well, probably try running away tbh.

 

How do you sneak attack yourself, and wouldn't the other you be trying to sneak attack you too?    I see rogue vs. mirror rogue likely just running away from each other.

 Depends on if the DM is allowing tasha's class features. Careful Aim + a crossbow or other ranged weapon could turn rogue vs rogue into a sniper duel as they trade attacks fishing for crits. 

Quote from Nyr_Ventus >>

Quote from MidnightPlat >>

Quote from CatDetective >>

Since I play a rogue, I can deal FAR more damage in one round than I can take, so... provided I make that first hit count? Jack can take out his evil double. But if he biffs that first roll, then he will... well, probably try running away tbh.

 

How do you sneak attack yourself, and wouldn't the other you be trying to sneak attack you too?    I see rogue vs. mirror rogue likely just running away from each other.

 Depends on if the DM is allowing tasha's class features. Careful Aim + a crossbow or other ranged weapon could turn rogue vs rogue into a sniper duel as they trade attacks fishing for crits. 

Fair play.  In these match ups I'd houserule it that tied initiative is just that a tie so you could have the rogue's bolting themselves out simultaneously.  

Still I see more cat and mouse with the two rogues stalking each other, which be even more tedious if they're stalking each other at range.  

For my rogue it would probably end up as: Hide (behind tree/terrain) Sneak Attack,

Hide, Sneak Attack.

Each coming back into view by shooting at the end of turn and being target-able during their opponent's turn. 

They both would have boots of elvenkind and +11 to stealth, so this could go on for a while. 

Talos 1. (Casts hex)

Talos 2. Oh no you don't (casts Fiendish Vigor and gains 8 temporary HP)

Talos 1. (Fires revolver and misses) 

Talos 2 Ok, two can play this game (Fires revolver and misses horribly)

Talos 1. Nerd (Runs up and and casts Agonizing Blast which promptly misses)

Me. (Changes d20)

Talos 2. (Gets within melee range and swings his longsword towards the double's neck. Rolls a nat 20. Deals 17 damage.

Me. (....)

Talos 1. Ouch, here's Hellish Rebuke (he succeeds the save and takes 3 damage plus a Agonizing Blast to the face which deals... Well... Nothing.)

Talos 2. (To quote my DM) Pathetic. Mortal. (Agonizing Blast rolls 19, which is our armor class. As per house rules it is a glancing blow. Half damage comes out to... Ah. It- it's 8, so he's down. 

I don't have it in me to roll death saves, so doppelganger won this one. 

I almost always play LN, so there is no evil opposite.