Pint-Sized Slasher mask

The Pint-Sized Slasher Gear, is obtained during the Tranquility Lane quest, if you decide to help Betty to kill all residents of Tranquility Lane. The gear consists of a knife and a clown mask. They are located in a doghouse, and are automatically equipped when you receive them.

The knife that you receive for this portion of the quest has a lot more power than a normal knife - more than twice any other knife in the game - and a very high chance for critical hits.

At the end of the quest, these items are removed from your inventory automatically.

Trivia
One of the newspapers shown when loading saved games mentions 'The Pint-Sized Slasher' in a side story. As well, the full article can be accessed via the Capitol Post newspaper office in L'Enfant Plaza. This gear, while undoubtedly not an easter egg by itself, may be a nod to Halloween, as Michael is shown at the beginning of the movie as a kid with a clown mask and a kitchen knife slashing up his sister.