Here is the full list of all 16 Demons with Shotguns achievements.
You kept killing yourself.
Flawless Victory!
You're an a' hole with how much you taunt.
You don't seem to understand how ammo pickups work.
You completed Ghosts n' Nomeds.
You used 10 tarot cards in one match.
You jumped 100 times in one match.
You earned a Antichrist kill streak.
You collected 500 souls!
You earned 5 Double Kills.
You earned 3 Monster Kills.
Fighting for scriptures.