REQ high investment so For this build im using w/frost (Hard cc and 175 efficient / Biting frost build) and also stacking primary frostbite to deal upfront 2.5 M burst alternative w/o CD and CC riven

frost build ! https://overframe.gg/build/535492/frost-prime/ice-harrow-bitting-frost-dont-try-this-is-just-for-lolz/ !

RIVEN STATS PRIORITY

DAMAGE
FIRE RATE
TOXIN

Honorable mentions
MULTI SHOT
CC

why Toxin? - to get corrosive effect since low strength and better scaling than CC

No CD why? - i'm using primary frost bite gives you 120% CD / 90% Multi shot, plus the new cold changes addtional 20 - 50 CD % (Eximus 4 max - mobs 9 max) on enemy and incarnon form / [Frost] augment Bitting Frost it's just overkill waste stat.

ARCANE PICKS

PRIMARY FROSTBITE - amazing arcane for shotguns cuz multishot and CD.
SHOTGUN VENDETTA - Double dips incarnon form also multi shot and reload speed.
PRIMARY DEADHEAD - 350 base dmg% if your riven has CC/CD optional.

FOR FRAME ARCANE

Arcane Avenger more CC but requires Exilus (Combat Discipline) to balance Primary Frostbite, or Arcane Acceleration if you have more CC on riven.
2nd arcane any for survival or quality of life arcane.

PLAYSTYLE / HELMITH

Use Avalanche (ability 4) for 6 cold procs so u only need 7 enemies effect cold it is enough to max stack for arcane or use ice wave (ability 2) EZ,
then cast Energize Munitions for extra mags (optional you can use other better helmith like air burst/nourish/condemn.[Frost]),
shoot and repeat.