The Full Head of Steam, Gentle Munitionne of Leisure, Frontline Field Recorder, The Skull Island Topper, Proffessor Speks, The Bombonicon, Mildly Disturbing Halloween Mask, Horseless Headless Horsemann's Head, The Monoculus!, Alien Swarm Parasite, Spiral Sallet, Bolt Action Blitzer, The Flamingo Kid, The Triclops,
I'll try and explain how you unlock these.
The Full Head of Steam and the
Gentle Munitionne of Leisure are each earned by completing the achievement milestones for the achievements of their respective maps: Foundry for Full Head of Steam and Doomsday for Gentle Munitionne.
The
Frontline Field Recorder is earned by completing one of the replay achievements where you get X views on a single replay uploaded to YouTube via TF2. There are ways to cheat this, like going into the replay file and spoofing the video ID for one with lots of views.
The
Skull Island Topper,
Professor Speks,
Bombinomicon,
Mildly Disturbing Halloween Mask,
Horseless Headless Horsemann's Head, and
MONOCULUS! can all be earned by defeating a Halloween boss on their respective map during the Halloween event. (Check the items' pages on the
Team Fortress Wiki.) Usually you enter an area of the underworld of the map after defeating the boss, then race other players to reach the end, where the hat resides.
The
Alien Swarm Parasite,
Spiral Sallet,
Bolt Action Blitzer,
Flamingo Kid, and the
Triclops are earned by completing achievements in other games. The Parasite is earned from a lesser known Valve game, Alien Swarm. The Spiral Sallet is from Spiral Knights; The Bolt Action Blitzer is from some game called CrimeCraft GangWars; and the Flamingo Kid and Triclops come from Super Monday Night Combat.
dont forget The Party Hat
The
Party Hat is obtained by playing TF2 on the date of the release of the original Team Fortress (usually referred to as Team Fortress's birthday by Valve) This happens around August 23rd - 24th.