Mule Spam

The term comes from the ROBLOX game The Wild West.

It is used for people who spam various shotguns in the game but specifically the Mule Shotgun. "Mule Spammer" is used as an insult, similarly to "Guycott Spam" and "Fan Fire Spam" when someone only uses weapons that require no aim.

Mule Spammer: L get better you're trash kid you have auction guns and died to a new player
Player: Shut up you mule spammer