An unused head model with 3 different skins for the Heavy robot (with red, blue, and yellow eyes) can be found in the files for Team Fortress 2.

The concept art for the Demoman originally showed him as a stereotypical Scottish person, with white skin and red hair. This was dropped because the developers thought he lacked originality and needed to be different from the other classes.

While Rottenburg is said to have been the Medic's hometown, his official profile previously stated that he was raised in Stuttgart, Germany.

The Ubercharge effect produced by the Medic in the "Meet the Medic" trailer is only possible with the stock Medi-Gun, but the Medi-Gun he is using is the Quick-Fix. Valve explained this in the "Uber Update", saying that the Quick-Fix's Invulnerability function shorted out after it's first time use.

The Ap-Sap, a sapper replacement for the Spy, is a reference to Wheatley, a main character in Portal 2, even having the same voice actor, Steven Merchant, voice the weapons sound files.

The "Unusual" effect, "It's A Secret To Everybody", is a reference to The Legend of Zelda, where the phrase has appeared repeatedly.

The death sounds in the "Meet the Engineer" trailer are different to that of the final game. This is most noticeable at 0:38, when there is clearly a Sniper on the rocks, but when the sentry gun shoots him, the death sound is that of a Soldier. Additionally, when an off-screen class yells "MY ARM!" at 0:54, it sounds like a Scout yelling, but the arm is clearly that of the Sniper.

The second trailer for Team Fortress 2 shows gameplay footage of each class, except for the Medic. However, the Medic does make two appearances in the video; once at 1:47, on the left, and once again at 1:50, he can be seen behind a wall.

The trailer also shows many sound and weapon changes. Some of these include the Scout using a weapon called the Nailgun, which was replaced by the Scattergun, and the Demoman can be seen throwing an pack of Dynamite, which was later replaced by his Stickybombs. Every class, including the Pyro, uses generic scream sounds for taking damage and dying, including the infamous Wilhelm scream.

In the "Meet The Sniper" trailer, the sniper pokes a bobble head and says "Boom, headshot." The bobble head is a reference to the Team Fortress Classic gamemode "Assassination", in which a group of snipers must kill a V.I.P. to win, and the phrase "Boom, headshot" is a reference to an internet mockumentary series called Pure Pwnage, in which a character called FPS Doug exclaims the phrase throughout.

Many of the AI bots in the game are named after references to Team Fortress 2, Valve's other works, and computer programming. Many of these names were requested by users on the Steam forums.

Due to its close resemblance to the ADAM Harvester from the Bioshock series, Valve requested permission from 2K Games to add the Vita-Saw to the game. However, due to copyright reason, Valve can't sell the Vita-Saw in the Mann Co. Store.

S.E.D, the acronym of "Sandvich Edible Device", is also the acronym for the Sozialistische Einheitspartei Deutschlands, the Communist governing party of East Germany from October 1949 to March 1990.

The weapon 'Blutsauger' has 2 unused, team-colored models for a syringe projectile. As it is not used, it instead uses the same projectile as the other Syringe Guns.

The wooden section of the Liberty Launcher's barrel has a crack on it, referencing the famous Liberty Bell.

Inside the Virtual Viewfinder's model is a screen that reads "Game Over".

The Natascha's wind up sound file is used by the forklift in Left 4 Dead 2.

There is an unused Kill Icon in the game that suggests the Taunt item 'Shred Alert' was once planned to be a Taunt Kill, meaning that players within it's radius would be killed, similar to the Pyro's Armageddon Taunt.

The level on the "Candy Cane" weapon is 25, referencing the date of Christmas.

The Spy revolver "L'Etranger", meaning "The Stranger" in English, is named after a book of the same name written by Albert Camus, in which an emotionally detached french Algerian murders an Arabian man using a handgun. The main character is mainly considered a sociopath due to his cold hearted nature, similar to that of the Spy.

One of the taunt kills for the Pyro is called "Hadouken". This is a direct reference to Street Fighter. The audio and kill icon further support this, although it's hard to understand the audio, but it does sound like the Pyro is saying "Hadou-Ken!".