Sword and Shot's Melee Assassin 611 dmg in one turn (5e Optimized Character Build)
From D&D Wiki
Optimized build ready-for-game
See this sheet .For informations about the symbols i used, see "other" box. It shows what to get at every level of your campaing to maximize the efficiency of this build.
How damage works
This build is based in using features that adds damage dies to your attacks, than doubling these dices with Assasinate feat's guaranteed crits. You will get these feats by multiclassing to Bard, Paladin, Warlock and Rogue.
Eldritch Invocation - Eldritch Smite (Warlock - Pact of the Blade lvl 5)
This feat (or kind of) is the foundation of the consistency of this build. It makes every creature that is Huge or smaller knock prone, making all of your subsequent attacks gain advantage (wich will likely be sufficient to make all of them hit), so make sure to use this as your first attack (wich already have advantage from assasinate feat). Plus a 5d8 that will crit (10d8) will do some harm...
Divine Smite (Paladin lvl 2)
This feat brings the most part of the damage with it. A massive 14d8 damage through 3 attacks that will crit (28d8), almost a crime to the humanity.
Sneak Attack (Rogue lvl 1)
You will get this anyway, so... it's just a bonus 2d6 that will crit (4d6), but it actually helps in the subsequential turns of combat (and costs nothing)
Psychic Blades (Bard - College of whispers lvl 3)
Another bonus, 3d6 that will crit (6d6) won't hurt (you), and u will burn only your inspiration dies.
Marial Adept (General)
If u want a little more damage, take any maneuver that adds the dice (1d6) to the damage roll and add it to your first attack (2d6 on crit).This feature is optional, you can take +2 charisma instead to make better rolls in your social interactions and deliever your spells that need saves with a little more realiability (they are few, but are very useful).
I tried to make all the resources used in the combo renewable to keep the charater useful in more the one encounter per day. To do that, i had to make the character a short rest dependant. With your warlock levels you get 2 4th lvl(level that maximize divine smite's damage) spells slots, that recharge when you make a short rest, also in level 5 of bard, your Bardic Inspiration uses, get recharged within a short rest as well, like many other feats that i choosed in the sheet of the link. So, if u don't need the full damage of the combo, just use the renewable resources and take a short rest
Ok, lets get to the fun part, deal the damage. First i will make some explanations that i didn't made above:
1- I got 5 lvls of bard and 4 of paladin, besides everything else, to have an additional spell slot lvl 4, and 3 spell slot lvl 3. Those Spells slots will be burned to uses of smites in 3 (or 4) different attacks in the same turn, and for the preparation of the combat
2- To get those 3 attack i needed the Eldritch Invacation - Thirsting Blade, with this, i can make 2 shortsword attacks with my action, and use a second short sword to attack with my bonus action.
3- If you have time to get prepared before attack the enemy, use the Shadow Blade spell with 3rd lvl spell slot to add 3d8 (6d8 on crit) instead of the 1d6 (2d6 on crit) to your bonus action short sword attack.As well, will help if any ally cast haste on you, or you drink the Potion of Speed, with this you can attack again with the shadow blade and use another 3rd lvl spell slot to deal another divine smite adding a total of 7d8 (14d8 on crit) for the damage... that is A LOT.
4- If your DM gives you a magic item of your choice, or if you want one by xanathar's guide to everything way of buying magic items (i predicted this, and the character have expertise in persuasion), get a Flame Tongue shortsword and make it your pact weapon, u will attack twice with it dealing 3d6 (6d6 on crit) instead of the 1d6 (2d6 on crit) of a normal shortsword PER ATTACK, totalizing an increase of 4d6 (8d6 on crit) in damage.
Now that i clarified this, lets start with the combo
For the First attack, you will need, obviously, surprise the enemy too guarantee the crits and the advantage. Burn 4th lvl spell slots for Eldritch Smite (that one is very important for the advantage on next attacks) and Divine smite, use your Bardic Inspiration in the Psychic Blade feat as well, and (if you have) the maneuver of you choice.
1d6 (shortsword), if prepared 3d6 (Flame Tongue) + 2d6 (sneak attack) + 3d6 (Psychic Blade) + 5d8 (eldritch smite) + 5d8 (divine smite) + 5 (Dex mod.) + CRIT
Total: 12d6 (16d6 if prepared) + 20d8 + 5
Now we get the second attack of Thirsting Blade with advantage from eldritch smite, lets continue:
1d6 (shortsword), if prepared 3d6 (Flame Tongue) + 5d8 (divine smite) + 5 (Dex mod.) + CRIT
Total: 2d6 (6d6 if prepared) + 10d8 + 5
Still with advantage, and our 4th lvl spells slots are over... it's time to use 3rd lvl spell slot for 4d8 divine smite damage, and this attack uses a bonus action, so Shadow Blade as well:
1d6 (shortsword), if prepared 3d8 (Shadow Blade) + 4d8 (divine smite) + CRIT
Total: 2d6 (6d8 if prepared) + 8d8
Haste Attack (only if prepared)
This attack can use divinity smite with 3rd lvl spell slot, and we will use Shadow Blade over Flame Tongue for the bigger dice:
3d8 (Shadow Blade) + 4d8 (divine smite) + 5 (Dex mod.) + CRIT
Total: 6d8 + 8d8 + 5
Turn's total damage output
I did the calculations with the LudicSavant and AureusFulgen's DPR Calculator, these guys are awesome, thanks for making this tool :)
So, we have a total of:
16d6 + 38d8 + 10 damage, that deals an Average Damage of 237, and a Maximum Damage of 410 in this turn.
So, we have a total of:
22d6 + 58d8 + 15 damage, that deals an Average Damage of 353, and a Maximum Damage of 611 in this turn.
Congratulations, now you have the potential to OTK (one turn kill) any Monster (except for Tarrasque and Zariel) that WotC have created. Unfortunaly, the odds are against you if the Crature is Gargantuan and have more than 243hp (DPR 243,6 without advantage), or if just have more than 310hp (DPR 310,1 with advantage) considering AC 20 for both. Don't forget about the absolute counters of this build: Immunity/Resistance to Radiant, Force and Psychic damages.
The complete build is in the sheet in the "Optimized build ready-for-game" section, there you can see the entire utility that the build have to apply the combo, it also have the order to take each spell or feat or what ever from lvl 1 to 20. I'm brazilian, so my grammar isn't a masterpiece, feel free to correct me :)