Long story short; I have a character at the ready for my next campaign (whenever it happens) that involves channeling elemental damage through his weapon, and combining it with his martial prowess.  So far, Blood Hunter is the only option that even comes close to the idea of this character, what with the Crimson Rite damage... but Battle Master more reflects the fighting style I was thinking for him.  With that in mind, I thought of a VERY bizarre (and more than likely divisive) solution to this collision of concept and available options; what if I could just replace the damage type of the Superiority dice damage with elemental damage (acid, cold, fire, lighting, thunder)?  Maybe it could be limited to a single element per day/long rest?  I could really use the thoughts of those more experienced than me, so thanks in advance for any answers that can be provided!

PS: no need to go into too much detail regarding complex calculations.  If you think this idea is OP, than that's fine, but please don't write an essay about why; I won't be able to understand most of it.

The single least resisted damage type in 5e is “Bludgeoning, Piercing, Slashing from a magical attack/source/weapon.” (The next least resisted are Force, Psychic, Radiant, and Necrotic to round out the five least resisted/immune damage types in this edition.) So technically speaking, even if you have nothing more magical than a staff of adornment or a moon-touched sword, a Battle Master’s maneuvers that add their Superiority die to the damage roll as additional “B, P, S from a magic attack” already add the “most OP damage type” in the game. So if you switch it to “elemental damage” (Acid, Cold, Fire, Lightning, Poison, Thunder), it would technically be kindof’a nerf. Yeah, as a DM, I’d allow it.

Thanks!  Also, cool information to know regarding damage type resistances.  :)

Sure thing. You can even pitch it to the DM in those terms if you need to. Like, could say something like this and still statistically be a slight nerf (if you guess wrong):

Whenever you add a superiority die to a damage roll with a magic weapon or a piece of magic ammunition, you can choose for the damage to be one of the following types instead of the weapon’s damage type: Acid, Cold, Fire, Lightning, Poison, or Thunder.

Ooooooh!  I like this a lot!

Quote from IamSposta >>

The single least resisted damage type in 5e is “Bludgeoning, Piercing, Slashing from a magical attack/source/weapon.” (The next least resisted are Force, Psychic, Radiant, and Necrotic to round out the five least resisted/immune damage types in this edition.) So technically speaking, even if you have nothing more magical than a staff of adornment or a moon-touched sword, a Battle Master’s maneuvers that add their Superiority die to the damage roll as additional “B, P, S from a magic attack” already add the “most OP damage type” in the game. So if you switch it to “elemental damage” (Acid, Cold, Fire, Lightning, Poison, Thunder), it would technically be kindof’a nerf. Yeah, as a DM, I’d allow it.

 Just want to note that you need to consider vulnerabilities as well in these kinds of comparisons. While magical BPS is almost never resisted, very few things are vulnerable to them.

This magical battlemaster, knowing that tomorrow he will be heading into the Icy Caverns of Freezing Doom, can make an educated guess that fire damage will not only not likely be resisted, but will very possibly deal double damage. If you play in the type of game that favors preparation and research before an adventure, this could definitely be an upgrade.

Quote from scatterbraind >>

Quote from IamSposta >>

The single least resisted damage type in 5e is “Bludgeoning, Piercing, Slashing from a magical attack/source/weapon.” (The next least resisted are Force, Psychic, Radiant, and Necrotic to round out the five least resisted/immune damage types in this edition.) So technically speaking, even if you have nothing more magical than a staff of adornment or a moon-touched sword, a Battle Master’s maneuvers that add their Superiority die to the damage roll as additional “B, P, S from a magic attack” already add the “most OP damage type” in the game. So if you switch it to “elemental damage” (Acid, Cold, Fire, Lightning, Poison, Thunder), it would technically be kindof’a nerf. Yeah, as a DM, I’d allow it.

 Just want to note that you need to consider vulnerabilities as well in these kinds of comparisons. While magical BPS is almost never resisted, very few things are vulnerable to them.

This magical battlemaster, knowing that tomorrow he will be heading into the Icy Caverns of Freezing Doom, can make an educated guess that fire damage will not only not likely be resisted, but will very possibly deal double damage. If you play in the type of game that favors preparation and research before an adventure, this could definitely be an upgrade.

 Damage vulnerability is actually pretty rare in 5e. For fire damage, it's mainly just plants and creatures containing vegetable matter (like Mummies), but only a handful of cold-environment creatures. (Fewer undead are vulnerable to radiant damage than you'd expect, too.) On the other hand, a Skeleton is vulnerable even to non-magical bludgeoning damage. Either way, it's worth packing damage types less likely to be resisted.

Most “Fire” creatures are resistant to Cold Damage or don’t hav anything special about cold, and most “Cold” creatures are also resistant to Fire Damage. (At least it usually seems that way to me. But I might be wrong.)

It is true that I hadn’t considered Damage Vulnerability. Maybe instead it would be better to make the Elemental Damage it’s own Maneuver.

Quote from IamSposta >>

Most “Fire” creatures are resistant to Cold Damage or don’t have anything special about cold, and most “Cold” creatures are also resistant to Fire Damage. (At least it usually seems that way to me. But I might be wrong.)

It is true that I hadn’t considered Damage Vulnerability. Maybe instead it would be better to make the Elemental Damage it’s own Maneuver.

 I think it's fine as is.

Depending on how much latitude your DM gives you, there was a UA 1st-level artificer spell that didn't make the cut called Arcane Weapon:

1st-level transmutation

Casting Time: 1 bonus action
Range: Self
Components: V, S
Duration: Concentration, up to 1 hour

You channel arcane energy into one simple or martial weapon you’re holding, and choose one damage type: acid, cold, fire, lightning, poison, or thunder. Until the spell ends, you deal an extra 1d6 damage of the chosen type to any target you hit with the weapon. If the weapon isn’t magical, it becomes a magic weapon for the spell’s duration.

As a bonus action, you can change the damage type, choosing from the options above.

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, you can maintain your concentration on the spell for up to 8 hours.

Spell Lists. Artificer

Maybe a Variant Human with the Artificer Initiate feat, and that as the spell choice, could then fit with your Elemental Battle Master.