which was revealed as a co-op mode on August 15, 2012. Marketing and microtransactions Valve had provided other promotions to draw players into the game. Valve has held weekends of free play for Team Fortress 2 before the game was made free-to-play. Through various updates, hats and accessories can be worn by any of the classes, giving players an ability to customize the look of their character, and extremely rare hats named "Unusuals" have particle effects attached to it and are only obtainable through opening "crates" or trading with other players. New weapons were added in updates to allow the player to choose a loadout and play style that best suits them. Hats and weapons can be gained as a random drop, through the crafting/trading systems, or via cross-promotion: Limited-edition hats and weapons have been awarded for pre-ordering or gaining Achievements in other content from Steam, both from Valve (such as Left 4 Dead 2 and Alien Swarm) or other third-party games such as Sam & Max: The Devil's Playhouse, Worms Reloaded, Killing Floor, or Poker Night at the Inventory (which features the Heavy class as a character). According to Robin Walker, Valve introduced these additional hats as an indirect means for players to show status within the game or their affiliation with another game series simply by visual appearance. The Pyro, Heavy, and Spy all function as a single playable character in the PC release of Sonic & All-Stars Racing Transformed. The Pyro, Medic, Engineer, and Heavy appear as playable characters in Dungeon of the Endless. The Pyro was added as a playable character to Killing Floor in 2010, along with appearing as a henchman in the 2021 game Evil Genius 2. The game's first television commercial premiered during the first episode of the fifth season of The Venture Bros. in June 2013, featuring in-game accessories that were created with the help of Adult Swim. Items and economy In Team Fortress 2, players can trade with others for items such as weapons and cosmetics. This functionality was added in the 2010 Mann-Conomy Update, alongside being able to purchase items through an in-game store with real money. Operating largely through informal gray markets before the introduction of the official Steam Community Market, trading items made players susceptible to fraud. Team Fortress 2 features an in-built item valuing system known as an item quality, assigned to a given instance of an