Given how tricky it is to add custom weapons to Strife, it replaces the standing assault gun pickup and uses the same ammo type as the Mauler. It basically acts like a slightly weaker version of the Mauler's primary fire, but uses half the ammo. Eriance's original Demon Eclipse shotgun seemed like a good fit, so I decided to recolor it and then add the Strife guy hands that JustinC had made for the shotgun used in Weasel's Strife mod. Further credits can be found inside of the .pk3 file.
Here's the sprite sheet I made for those that would rather use it for something else:
Spoiler:I'm going to work on an enhanced version next, which will be uploaded When It's Done (TM).
Edit:
Here are the credits for the mod:
Eriance - Demon Eclipse Shotgun
JustinC - Strife Guy Hands
Rogue Software - Muzzle Flash
Snarboo - Recoloring and various edits
Feel free to do whatever you want with this!
Edit 2:
Version 2 of the Thrasher has been released! It now takes accuracy and stamina into account. At the highest levels, there should be no weapon recoil, and the spread should be about as tight as Doom's shotgun.