[Rhino]

Honestly, I don't know about primary weapon, because I'm working on my Tigris, but I use Kunai for my secondary, and they will shred just about EVERYTHING I fight. Even in Damage 2.0, I'm still doing almost 300 damage to infested before counting in elemental effects. And I have, currently, 160% multishot. And a 5.9 fire rate. They're crazy fast and powerful.

[Pathogen Rounds / Toxic Pistol Mod, How Ultramegasuperrare Is This Bugger?]

I can tell you, with absolute certainty, that it does NOT drop from Toxic Ancients or Ancient Disruptors. Still working on scanning other enemies for info though.