Check the mod priority guide:
https://docs.google.com/spreadsheets/d/1ty239kyJbBs1sLhTo1JvSWuN0mIJsK1nwVdI6OLLtXo/view?rm=minimalThe time-tested Nagant Revolver brings a solid MOD to the table, packing both good offensive and defensive support.
Her main upgrade lies in her Skill 2,
Seven Tone Paean. This skill gives all allies a nice buff to Damage and Accuracy for 4 seconds after every 7 shots (including before the first shot at the start of battle) . On top of this, her already legendary Damage/Crit tiles get even stronger, and her first skill sees a further bump in effectiveness.
All in all, a great MOD for any battle you need a boost to both power and survivability. In particular, M1895 can help lower armour requirements for some SG fights or boost the effectiveness of HP shields (although TEC-9 can be a different budget option if you don’t want to pay the MOD cost). Do note that the defensive nature of Nagant Revolver’s first skill does mean she won’t typically be the first choice for general use.
You will want to get her to
MOD2 for her Skill 2. Her Special Equipment is not worth the cost (though her MOD3 art is amazing).
Nagant's SPEQ-set is quite strong, making her a competent damage buffer at Night on top of everything else she already does. However, her full performance is still limited to Night Battles, and with few relevant maps, this set is optional.