Firerate on the [Knell] is like firerate on [Mesa]'s 4th where because you have an infinite magazine it is a direct DPS increase of 90% with Anemic Agility (not including the -damage).

Cascadia Flare and Galvanized Shot both work a lot better than you'd assume looking at the numbers because Death [Knell] stacks up status chance very fast.

Not exactly a defined Riven slot anywhere, the most removable slots are Galvanized Shot and Primed Pistol Gambit but of course if your riven has things like fire rate/crit damage/heat then other mods are possibly worth replacing instead.

Bane mods aren't necessary at all.

The [Knell] is weird, it's not a room cleaner and it's not gonna be anyone's main weapon ever really but by essentially being the highest DPS weapon in the game even if gimmicky in use it's worth carrying in the back as a solid big bad eraser. It's really good for Archons and other bosses, and when I'm running the room clear type weapons it's a good deleter of Acolytes and Disruption enemies. This isn't to say you can't rely on the weapon far more, you can play any tank/invis frame and just walk around mowing down whatever runs at you