Was available as a random end-of-mission reward from accomplishing the Endurance challenge of the Emergency ExitTactical Alert.
Fanged Fusillade is now offered as a periodic item for sale by Baro Ki'Teer costing 375375 and 150,000 150,000 to purchase. Note that Baro Ki'Teer's stock changes with each appearance, and this mod may not be available on a succeeding appearance.
When calculating total raw damage, a weapon will require a Slash damage percentage equal to 75% of its total base damage to equal the raw damage increase provided by a standard elemental mod (which increases corresponding elemental damages by 90%). The higher the Slash damage percentage over 75%, the more viable this mod will be as opposed to an elemental mod, and vice versa for lower values. These calculations only pertain to raw damage, and do not take into consideration enemy armor/flesh/shield damage multipliers.
Dread, Flux Rifle, and Miter are the only weapons that can use this mod effectively, due to having above 75% Slash damage.