Infected
It started from developer. To get it you should play in co-op with infected players.
Mandragora's Respect
Complete the Unbalanced Build challenge
Spider King
Kill the Spider boss without taking any damage
Devoured Alive
Die in the Viscera location
Butcher
Kill 100 enemies with buzz saws
Double Dismemberment
Kill two enemies simultaneously with a buzz saw
Bloodbath
Kill 100 enemies with a Double Buzz Saw
Adrenaline
Complete the "On the Razor's Edge" challenge
Adventurer
Explore all rooms in 3 consecutive locations
Lab Worm
Kill the Worm boss in the Secret Lab
Top of the Food Chain
Kill the boss in the Organism location
Wasp Lord
Kill the Wasp boss
Wasp Exterminator
Kill 10 enemies with a Wasp
Trusty Friend
Kill the Dog boss
Bro
Resurrect an ally on your team 3 times
Life of the Party
Resurrect 3 different allies in the same room
Risen from the Ashes
Complete the Furnace without falling below 50% health
Victim of Experiments
Pick up 3 mutations in the Secret Lab
Matters of the Heart
Complete the Viscera location
Maze Runner
Complete the "Labyrinth" challenge
Makeshift Means
Kill 10 enemies with a flying barrel
Burglar
Unlock all doors in all locations
Shopping
Upgrade the store 1 time
Shopaholic
Upgrade the store 10 times
Heads Off
Kill the Tenheads boss in the Furnace
Shoulder to Shoulder
Take an elevator down to the Organism location with a team of 3 friends
Born on the Inside
Unlock a new mutation in the Viscera location
Dark Corner
Go down to the Catacombs
Brains on the Wall
Kill the Brain boss
Rage Against the Worm
Kill the Worm boss while the Rage skill is active
Tainted Blood
Complete the "Survival" challenge
Keeping Calm
Find 2 stun guns in a single run
Commotion
Kill 4 enemies in one room without hitting them directly
What the Hell Happened?
Kill all enemies in one location without hitting them directly
Spoiled Brat
Resurrect with the help of an Embryo 5 times
Factory Monster
Unlock a new mutation in the Factory
Lab Monster
Unlock a new mutation in the Secret Lab
Fiery Monster
Unlock a new mutation in the Furnace
Frozen Monster
Unlock a new mutation in the Freezer
Brotherly Grave
Die alongside one or more players
Triple Penetration
Kill 3 enemies with one hit
The Magnificent Four
Complete a successful run with four players in co-op