Hello, the more you go up in the difficulty, the more elemental resistances the enemies get. Is there anyway to nullify it (with a mod or whatever) ? Because in nightmare, you will do 1 point of damage depending of the element you are using.
unsure if there is a mod specifically for this, but if you're playing nightmare because you enjoy the challenge my suggestion would be to invest in crafting and carry weapons with different elemental attributes/runes (especially if you are a mage) into the field.
this way, you can switch the active staff before the confrontation without having to constantly travel back to skyhold. if you know beforehand which area will feature which type of mobs, that can also help offset resistances.
red templars have cold resistance, but take extra damage from cleansing runes. so, if you know this before traveling, carrying a fire staff with a cleansing rune would dominate.
before beginning the quest, having your mage equip a demon slaying rune to a staff with increased chance to crit/crit damage will greatly increase your damage potential despite every demon having a different elemental resistance.
for rogue and warrior companions, i recommend completely ignoring the elemental runes and instead using cleansing, corrupting, or demon slaying runes. if you're having trouble finding crafting mats for the higher tier runes, just throwing a superb or master of any of the above onto the tank/rogue you carry with you the most will help a lot.