Is there a way for a level 20 Barbarian to change the damage type being dealt by a weapon?

Question

Last night I was playing as my level 20 Barbarian, when our party encountered an enemy who was immune to all damage, unless it was of a specific elemental type.

This was particularly unfortunate for me, since my Barbarian deals exclusively in piercing and slashing damage. This resulted in me effectively standing around acting as a damage sponge while the party's spell-casters dealt all the damage.

While not a disastrous situation, it got me thinking:

Are there any ways to effectively change the type of damage I am dealing?

To be more specific, I am curious if there are any spells, enchantments, magics, magical weapons, etc which can change the type of damage a weapon's normal attack would have dealt. For example, my Barbarian's weapon deals slashing damage - I am wondering if there are ways to change the damage type into something else(eg into instead dealing fire or poison damage, or even piercing or bludgeoning).

I've read this similar question, but am playing 5e, not 3.5.

Answer 1

No.

There are no weapons that just straight-up switch their damage type like that, and no spells or class abilities that can allow it.

There are weapons such as a Flame Tongue or Frost Brand which can deal additional elemental damage of a particular type. Then there are weapons like a Sun Blade which exclusively deals Radiant damage instead of Slashing damage.

As was mentioned in the comments, spells like Elemental Weapon or runes from Storm King's Thunder also exist...but they, likewise, supplement your damage, rather than entirely changing the type.

There is also the Sun Soul Monk, who can elect to trade out their Unarmed Strikes for energy blasts that deal Radiant Damage...but this is an alternate form of attack, not actually changing a weapon's damage type.

Ultimately, if you want a weapon that can change the sort of damage it deals, you're in homebrew territory.

Tangential Advice

There's nothing wrong with supplementing damage with an Elemental Type, rather than replacing it entirely. At least then you're doing something to contribute to the damage dealt. Perhaps carry extra gear that lets you nonmagically mimic elemental damage types, such as Alchemist's Fire, Acid Flasks, Poisons, etc.

Answer 2

Possibly...

Though this would likely be type-limited to bludgeoning, piercing, and slashing, you may - at your DM's discretion - be able to leverage the Improvised Weapons rules. From the SRD:

Improvised Weapons

...

At the GM’s option, a character proficient with a weapon can use a similar object as if it were that weapon and use his or her proficiency bonus. An object that bears no resemblance to a weapon deals 1d4 damage (the GM assigns a damage type appropriate to the object). If a character uses a ranged weapon to make a melee attack, or throws a melee weapon that does not have the thrown property, it also deals 1d4 damage. An improvised thrown weapon has a normal range of 20 feet and a long range of 60 feet.

This offers an simple, RAW, DM-moderated way to handle usage of a weapon in a way that would change the type of damage dealt. One might bash an enemy with the hilt of a longsword as if it were a club, for example.

Answer 3

While the answer is yes, it is nearly impossible and depends on a lot of DM intervention and interpretation.

Your Barbarian can change the type of damage they do with their melee weapons.

Method 1: Appeal to the power of Wish

A wish spell can be used to temporarily transform your weapon into an energy type weapon for about 8 hours, which is in line with the same power scope as "grant up to 10 creatures you can see immunity to a single spell or other magical effect for 8 hours" and producing a non magical item worth up to 25,000 gp permanently.

This would thus create a temporary magic item, probably under 25,000 gp in value, of the rare/very rare class. Since the object doesn't last more than 8 hours before reverting, it isn't truly creating a magic item, just a temporary magic item like effect.

Rare/very rare weapon types include: frostbrand, flame tongue, and sunblade, but only the sunblade is specifically a total change in the blade type, rather that bonus damage.

Alternatively, you can use the power of your wizard buddy's wish (or the wish of his simulacrum so he doesn't lose the power to cast it) to allow you to temporarily grant your weapon the properties of a druid's Flame Blade, which more or less duplicates the power of a 2nd level spell.

Method 2: Use the DMG Creating a New Spell rules to import an old spell

There used to be some editions where a priest could temporarily grant the power to cast low level priest spells (in this case, flame blade would be the spell) but I do not believe that spell exists in 5e. However, the DMG has a section on creating spells. You could ask your DM to "create" a spell using the rules on pages 283-284 that creates a druid variant of the 4th level cleric spell Imbue with Spell Ability (which grants a few 1st level spells plus 1 second level spell), and also make it available to your party's Druid.

Then you would simply cast flame blade, which lasts 10 minutes and inflicts 3d6 fire damage, using melee spell attacks.

The problem with this method is the damage is not going to include anything like strength bonuses or enchantments your weapon previously had; it merely fulfills the visual of a Barbarian wielding what appears to be a slashing weapon (scimitar base) that actually deals fire (3d6).

In Hind Sight, if your DM allows you to import spells and then adjust them via the rules on page 283, then you can probably pull an existing spell from somewhere that does exactly what you want, and let your DM pick the spell level.

Recommendation:

I would recommend the Simulacrum/Wish for Temporary sunblade-esque or flameblade function for your current weapon. That at least, is close enough to using the Rules as Written to be sorta legal. The only drawback is most people consider anything to do with Wishes to be Rules as Interpreted - but they are still less RAI than importing new spells.

Sim/wish is a pretty hefty order, but you did say level 20, so it's not impossible.

Answer 4

As a DM, I always rule that you can use the hilt of your sword for 1d4+ [str] bludgeoning. I also rule that if your sword is thick enough (eg, not a rapier) you can turn the sword round and use the flat edge to do 1d6 damage without mods (since you could bend and break the sword). This isnt changing the damage type, as such, but it does provide you with a way of dealing a different type of damage with a different attack, using what you have.

This is a homebrew rule, but my players and I agree that this makes combat more realistic.