Starting a new campaign for my players, we are running Baldur's Gate: Descent into Avernus. Most, if not all of the creatures my players will encounter are resistant to non-magical physical attacks. Rather than give them standard magic weapons to bypass that, I noticed the new item type "hellfire weapon". Has anyone here ran the campaign and found if it states these weapons bypass devil/demon resistance? Has anyone house ruled it so that they do? What was your cost for hell fire weapons? How did they balance out? Thanks!

Hellfire Weapons are uncommon +1 magic weapons, so they bypass non-magical weapon resistance.

Uncommon magic items have a recommended price of 400 GP.

The only special attributes of the hellfire weapons compared to normal +1 magic weapons is that they glow with dim light in a 5 foot radius and anything killed by them has their soul sent to the river styx to be reborn as a lemure devil.

I could easily see a devil or night hag trading these weapons (be it for souls or favors), especially since the using the weapons to kill mortals will benefit the fiend in the long run.

All magical weapons bypass resistance to non-magical weapons, including common ones like moon-touched.

I don't understand these weapons. I would assume they are in violation of the Pact Primeval. I don't know how they are justified in a lore sense. 

Is the pact primeval even still canon in 5e? Mordenkainen's chapter about the Blood War makes no reference to it at all.

 It is not.

I can find evidence that they're at least magical, but can't find anything that says they are +1 to hit or damage?  They are cool but without a +1, not super appealing. 

Quote from jankygames >>

I can find evidence that they're at least magical, but can't find anything that says they are +1 to hit or damage?  They are cool but without a +1, not super appealing. 

 The idea behind them is that there are a lot of creatures in hell that are resistant to non-magic weapons. These are to give amother way to obtain weapons that can damage them.

Their damage on their page here on DnDbeyond is 1d#+1. I suppose they only get the +1 to damage, not to hit.
https://www.dndbeyond.com/magic-items/hellfire-weapon

Quote from Jaysburn >>

Their damage on their page here on DnDbeyond is 1d#+1. I suppose they only get the +1 to damage, not to hit.
https://www.dndbeyond.com/magic-items/hellfire-weapon

 That is very likely a mistake on DDB's part since the description and sourcebook make no mention of extra damage. And the character sheets correctly display damage without an extra +1.

A little late to the party here, but a moon-touched sword from XGtE is also a magic weapon, at the low price of roughly 50 gp.