Charisma stacking, optional greater invis build for Ray of Frost-optimised damage gear.
Recommended to use a mod that changes/repairs Mourning Frost to be an actually competitive weapon. (Astarion’s origin maximises the attack hit chance and skill checks).
Rhapsody only loses 1 (2 with wet) damage, but can provide a nice guaranteed crit and the +3 attack roll, which is quite significant if we go with the Spellmight. Naturally, Marko-Mourning dual-wield is also great, but you’d lose a bit too much hit chance with active Spellmight.
Lvl 8 Cold Adept can be changed to +2 Char, if you’d like to get a crit immune helm (Helldusk, which also provides blind immune, so you can also abuse Darkness on top of the baselie built-in Greater Invis).
You can double down on it with another character using Markoheskir, either a frost double or an extra lightning spellcaster, because Evocation wizard lvl 10 gives you the spellcast modifier for all elemental cantrips, the Elemental Augmentation neck is also a general spellcast modifier bonus, however, Markoheskir damage boost is proficiency-based, and you can luck or savescum 2 chars with 24 char, but int maxes out at 22 with the Mirror bonus.
Arcane Bolstering is to go absolute nuts on the damage, also making use of the additional bonus action in a bit less resource-intensive way 🙂
If you go all the way to even sacrificing the mobility/ anti-slip boots for the +2 damage, then the final damage numbers on the Ray of Frost are these (with spellcast modifier damage bonus on Mourning Frost):
((4*7+3+2)+4*(2-8))=33+8-32 = 41-65 -> 82-130 on wet, so on a standard, non-haste turn with pre-wet targets or chilled from the previous turn, you can deal 246 damage minimum with a twinned + a single Quick casted Ray with a potential 390 max damage; the average being 318.
Considering that you’re using another bonus action for dashing to activate the boots, a pre-activated turn is even crazier, but also significantly more sorcery point demanding; alternatively, you can use a bonus action to chug down a haste potion -> turning a single ray from quick cast into a twinned ray from normal action.
Since endgame encounters operate in the range of 400-800 total HP pool of enemies, you can either completely clean up a smaller one in the first round, if you have a dedicated Raincaster or bottle-thrower.
