There are 4 guns in UBERMOSH

Purple
Gray
Yellow
Red

The Purple gun fires 1 larger bullet
The Gray gun fires 2 smaller blue bullets in a narrow spread
The Yellow gun fires 3 smaller bullets in a wider spread
The Red gun fires a very wide spread of 6 bullets

Walking over any gun will pick it up
Walking over any gun while carrying another will swap it for the one you walk over
The Red gun cannot be swapped out.

Bullets can hit multiple enemies

The sword is available to all classes except the gunner
The classless mod starts with the sword, but can pick up guns
The Kensei starts with the sword but cannot pick up any guns
The Warlock starts with the sword and the Red gun

The sword is used by pressing the left mouse button for all classes
The Kensei can also swing the sword by pressing the right mouse button
The sword swings in an arc, and will deflect all bullets it hits

Deflected bullets split in half, doubling the number flung back at the enemy

Mastering the sword is near mandatory for all classes that use it, because it is your only defensive option other than dodging
Mastering the sword IS mandatory for the Kensei because it is your only offensive option