Complete the indicated task to unlock the achievement.

Achievement	How to unlock
Agent G	Finish the full campaign with your friend!
Agent	Finish the campaign at any difficulty.
Blood Bath	Finish the campaign at ARCADE difficulty.
Butcher	Kill 666 enemies.
Catch'em All!	Collect all creature entries.
Chariot	Beat Chariot at the end of the first chapter.
Collector	Collect all items in a single campaign.
Dance Macabre	Nail down opponent's head with Pitter.
Deratization	Kill all rats in game.
Ender	Discover all three endings.
Full Armory	Collect all additional weapons available in the game.
Glass cleaner	Don't destroy any glass panels on chapter 2.
Granadier	Kill five enemies at the same time.
Hangedman	Beat Hangedman at the end of the second chapter.
Headhunter	Blow off 666 heads!
Hermit	Beat Hermit at the end of the third chapter.
Hero	Save a Scientist.
Invincible!	Finish the whole campaign without taking any damage.
Magician	Beat the Magician at the end of the fourth chapter.
Murderer	Kill a Scientist.
No ammo wasted	Finish a chapter without reloading with bullets in the chamber.
Normal ending	Finish the game with a final score below 62,000 and the last score digit not equal to zero.
Not this time!	Finish single chapter without taking any damage.
Partner	Finish any chapter with help of Player 2.
Penta-Kill!	Kill five enemies in a row.
Psychopath	Kill all the Scientists at any chapter.
Really?	Lose all credits and die.
Reinforcements!	Let Player 2 join the game while in a middle of a campaing.
Ringo	Knock up an enemy as high as possible.
Sadist	Devastate the opponent's body as much as possible!
Saviour	Save all the Scientists through the campaign.
Secret Room	Enter secret room on Chapter 4.
Swifty	Shoot down fifty enemy projectiles.
The House Of The Dead	Unlock all achievements of The House Of The Dead!
Third ending	Finish the game with a final score below 62,000 and the last score digit equal to zero.
Traveller	Discover all paths available in the game.
Triple-Kill!	Kill three enemies in a row.
True ending	Complete the game with a total score of over 62,000.
Try this!	Collect your first additional weapon.
Unwinged	Shoot all of the Hangedman's Devilions.
Who let the dogs out?	Knock back the Kenfis.