The Seal Mask is a cosmetic item found inside the Antique Halloween Goodie Cauldron, which is for all classes. It is a paper mask depicting a seal's face with crudely taped-on whiskers. When worn by the Demoman, the seal's left eye is taped out.
This item can only be worn around Halloween or during a Full Moon; at other times of the year, it does not appear in gameplay, unless the server has Halloween mode enabled. However, it can be equipped at any time and can still be viewed on the loadout screen even when it is not visible during games.
- The Seal Mask was added to the game.
- Removed "hat" equip region.
- The item description refers to the clubbing of seal pups to death, a controversial poaching method performed in several countries and commonly cited by animal rights organizations.
- The mask is based on a post on Steam Users' Forums  regarding the Summer Camp Sale. The post said, "the SUMMER SEAL ,WILL BEGIN soon????" From this post, seals made appearances in several of the promotional images for the sale. One of the mascots for the Steam Halloween Sale is seen wearing the Seal Mask as a nod to the thread. 
- Like several other Halloween hats, the Seal Mask's level references Halloween, which happens on October 31.
- The post by BurtonJ linking to the original "SUMMER SEAL" post.
- Another post by BurtonJ that has since been edited to remove the links.
- BurtonJ confirming the Seal Mask is a reference to that post mentioned before.