Potato Fools Day
Potato Fools Day was a promotional scavenger hunt arranged by Valve, to promote Portal 2, during the time surrounding April 1st, 2011. Killing Floor was one of thirteen indie games participating in the event. Among the changes and additions to Killing Floor during the update were a potato on the weapons list, the character biographies, and several achievements.
The potato added to the Trader weapon list cost £70,000 to buy and provided the achievement Uber Tuber to all players and spectators in the game upon purchase, providing the user wasn't on solo and only used whitelisted content. The game also opened a Steam browser page to the Aperture Science login page, to which the password was "failed experiments". The player didn't actually gain any sort of potato weapon to attack specimens with upon its purchase.
The model of dropped money was also changed to a potato.
 Buying the potato
In order to legitimately acquire the £70,000 required to purchase the potato one of the following situations could have been used:
- Playing on beginner difficulty on a listen server, not solo, with the faked players mutator enabled, set to 99 players, as a level 6 Berserker. Since there will be 800 specimens per wave all other classes will have ammunition issues.
- Leaving a single weak specimen alive at the end of a wave and healing a team mate as it damages them for the healing money. This tactic takes a very long time, and can also be used in conjunction with levelling the Field Medic perk.
- Playing on the map HeresyBeta3, due to it having a money room.
- Playing on Perklevelingultra, due to its money room, can get you the achievement in under three minutes.
“Congratulations you found the message
Good job puzzle hunter
Here is your clue
Sixteen and four is the way
Message transmission complete” —The decoded message
Of the six achievements originally added only one was originally achievable; Uber Tuber, for buying the potato. The other five were cyphertexts encoded using the Enigma cypher. These five cypher achievements were later changed into the level achievements for Aperture, and Not ASCII was changed to Glyphy with the description Glyph Glyph and later to the Golden Potato achievement.
 Character biographies
Another change to the game was the character biographies, which were changed during the April 4th update. During the April 8th update all but the biographies of DJ Scully, Mr Foster, and Paramedic Alfred Anderson were removed. The biographies for DJ Scully, Mr Foster, and Paramedic Alfred Anderson were encoded messages. DJ Scully's being in base64 for "the writer", Mr Foster's being a cypher, and Alfred Anderson's being hexadecimal code for "Alien 8 It. 2074 -4629 17". Following the April 12th update all character biographies were reverted back to normal except for Mr Foster and Paramedic Alfred Anderson. The biographies were as follows:
|Corporal Lewis||Summer Solstice|
|Lieutenant Masterson||Has anyone noticed that I'm in every game that Tripwire makes?|
|Police Constable Briar||My favorite color is Yelowwwwwwwwwwww|
|Police Sergeant Davin||So apparently the end of the world isn't all all it was cracked up to be.|
|Private Schnieder||Ah fuck off.|
|Sergeant Powers||In search of a caravan and some dags to live out his life in peace|
|Agent Wilkes||Imma monkey fightin killin machine up in this monday through friday place.|
|Foundry Worker Aldridge||I wonder what it says on my wrench.|
|Dr. Gary Glover||A132 - 417|
|Mr. Foster||I said, "One's sofa have deep counts," as I die.|
|Security Officer Thorne||Rawr, rawr rawr.|
|Lance-Corporal Lee Baron||Where'd I put that box of bomb parts?|
|Mike Noble||Has been known to say while reloading "Can't you see the Answer is always 42"|
|Harold Hunt||A current member of the A-Team.|
|Kerry Fitzpatrick||Where the wind blows, far two east settles the mind.|
|Trooper Clive Jenkins||35 short ones for an Irish meal.|
|Paramedic Alfred Anderson||41 6c 69 65 6e 20 38 20 49 74 2e 20 32 30 37 34 20 2d 34 36 32 39 20 31 37|
|London's finest characters|
|Chopper Harris||Two world wars, one world cup.|
|Kevo the Chav||Hit Tom. Kiss Ace!|
|Captain Wiggins||What's old, Brittish and farts a lot?|
|Reverend Alberts||Kenny Rogers? Is that you?|
|Harchier Spebbington||Ask Hey Vie|
|RED Pyro||Red > Blue|
|BLU Pyro||Oh great, a TF2 tie-in.|
|Bill "Baddest Santa" Weeks||If you can read this, you're probably an achievement whore. Just sayin'.|