What's the maximum number of damage types I can have in a single melee attack?

Question

Inspired by these two questions.

I am currently playing an Arcane Trickster that has a Flame Tongue Rapier and access to Booming Blade.

So I have:

• Piercing
• Fire
• Thunder

I am considering getting access to the Poisoner feat and Hex, adding Poison and Necrotic to the mix (with a ridiculous set-up sequence, I know).

This would leave me at 5 damage types in a single attack.

Is it possible to have more, across any class/subclass/multiclass (i.e., you're free to start with a new blank character)?

You can assume to get to level 20, and have access to items in the PHB, DMG, Xanathar, and Tasha. As in the case of my character, set-up can be spread over multiple rounds. Outside help is allowed, but I would prefer not.

Answer 1

13 out of 13 existing damage types, oh yeah

So, for the weapon of choice, take scimitar. Your race is Fallen Aasimar, because of necrotic shroud. For the class/subclass setup, take those:

• 4 levels of Fighter (Psi warrior)
• 4 levels of Paladin (any)
• 1 level of Warlock (Genie - Dao)
• 4 levels of Ranger (Swarmkeeper)
• 7 levels of Scribe Wizard (LEarning Booming Blade, Ray of Frost, Glyph of Warding)

For the feats, those are essential:

• Poisoner
• Gift of the Chromatic Dragon

As for items, well:

• Flame Tongue version of your shortsword
• Incense and powdered diamond worth at least 200 gp, for the glyph of warding
• Bag of Holding, for easing up transportation

This will give you following damage types on a shortsword hit:

• Slashing from scimitar
• Piercing from Gathered Swarm (3rd-level Swarmkeeper feature)
• Bludgeoning from Genie's Wrath (1st level Genie Warlock feature)
• Thunder from Booming Blade (Cantrip from Scribe Wizard list)
• Force from Psionic Strike (3rd-level Psi Warrior feature)
• Poison from applied poison (from Poisoner feat, as a bonus action
• Radiant from Divine smite (2nd-level Paladin feature)
• Necrotic from Necrotic Shroud (Aasimar race feature - must be activated before using a bonus action)
• Psychic from Wrathful Smite (1st level paladin spell - must be activated before using a bonus action, uses concentration)
• Acid from Gift of the Chromatic Dragon (must be activated before using a bonus action)
• Cold from Absorb Elements if you were hit with cold damage, which you yourself provide hitting yourself with ray of frost with your action surge
• Fire from your Flame Tongue Shortsword
• Lightning from Explosive Runes property from your Glyph of Warding, which you set to go off when you hit someone with your sword (You must do this before the fight, casting inside bag of holding to not be bound to 10 foot radius of place where you actually casted it)

So yeah, it is possible to deal all damage types in a single attack.