From Team Fortress Wiki
When equipped, players are able to see in Pyrovision; map textures are replaced with those of Pyroland, gibs and pickups are replaced with their counterparts from birthday mode, other players' voices become high-pitched, and other players laugh when injured or killed.
- The Balloonicorn was added to the game.
- [Undocumented] The Balloonicorn was added to the drop system.
- [Undocumented] Changed the Balloonicorn's item type from "Badge" to "Balloon".
- Fixed the achievement "The Great Deflate" not counting certain Balloonicorn items.
- The Balloonicorn is sometimes visible to players not in Pyroland.
- Before being officially added to the game, Balloonicorn was hinted at in the comic A Smissmas Story, on page 1, hanging on the tree.