Innate toxin damage, but modded heat damage combines with Shock Trooper to make radiation damage (we're not actually doing gas damage).

Works much the same as Knell Prime, advantages:

• Better riven disposition (1.1 vs 0.75 for Knell Prime), so riven stats are considerably higher.
• No need for headshot to proc Death Knell buff (mostly quality of life, but avoids some grief from Gantulyst's yellow orbs).
• Not being Knell itself, this bug is a non-issue: https://forums.warframe.com/topic/1337042-being-downed-while-death-knell-buff-active-makes-the-buff-not-proc-on-knell-prime-on-headshots-after-reviving
• Beam weapon, so multishot is a direct damage multiplier (instead of being discrete pellets with a probability distribution).
• Higher base firerate, so less need for modded firerate for fast limb breaks (allowing for more multishot to increase damage instead)
• Reloads itself and never runs out of ammo with Pax Charge (no need to sit through reload animation or use holster reload mods).

Disadvantages:

• Limited range of 28m, so can be difficult to hit upper limbs/capshots on Hydrolyst, particularly at long spawn. Mostly a non-issue with proper positioning, and hydro capshot can always just be done with [Zenith]. You can use the Gibber grip for 31 range at the cost of ~7.9% base damage, but this isn't really worthwhile. The exilus mod Ruinous Extension isn't an option as we need the -spread from Twitch and Reflex Draw to ensure the tentacles reliably hit limbs.
• Limited magazine of 43, so especially with high fire rate (Arcane Velocity, Amalgam Furax Body Count, etc.) you're more likely to run out of ammo on slow shield breaks. Pre-firing for ~0.6s is necessary for damage ramp-up as a beam weapon, so timing is a bit less forgiving than Knell (but far more forgiving than Pandero).
• Tentacles sometimes do not properly latch onto limbs (happens rarely with -spread exilus mods).
• Lower base damage and critical multiplier (the latter from the Death [Knell] buff), though the innate 5 multishot makes up for this.

Overall I've found it to perform at least as well as [Knell Prime] for limb breaks and have a bit better quality of life.