Oddity Suggestions:

[digital forge]

Globbler: Globs no longer bounce, but do not detonate on impact. Instead, they will roll downhill / roll around flat surfaces or time out. Glob size is multiplied for effect.

The Carver: Chance to drop your chainsaw on the ground, dealing damage over time in an AoE. Have to pull it out of the ground to get it back, damaging yourself in the process. Can lodge itself in an enemy. Should have a hefty HUD element pointing at it so you don't lose it. For the sake of Ouroboros, you automatically get it back on room clear and cannot drop it until the next wave starts.

Gunship cannon: Hold the cannon in front of you and shake the bullets out. Bullets come out at random intervals (higher fire rate to compensate) straight down regardless of where you're looking. Cannon can sometimes get clogged forcing you to sit through an animation or something instead of reloading.

[digital forge]

Jackrabbit: All stats (bounces, piercing, fire rate, magazine size, etc..) are converted into damage, press the shoot button to bop the enemy with the butt of your gun. Alternate firing methods get a melee version (flamethrower -> shoot a flame on-hit). Now people can have a double true melee build...maybe hold reload to throw it like a boomerang so they can kill quadcopters...

[topaz goblet]

Alternate Jackrabbit idea...
"Slug" Rounds:
Reduces pellet count to 1, but it instead scales projectile size, bullet speed, and damage. The primary fire launches a slug (the animal) that leaves behind a trail of slowing zones that deals acid damage which can be set on fire via flamethrower or other fire damage sources. (This won't hurt the slug)