Marcstick's knife is the only weapon Marcstick wields. It never made any appearances in the movie, only first appearing in the game. It also appeared in Slush Tile Rush. It might be inspired from the hidden blade from Assassins Creed.
Slush Invaders: Game
Marcstick uses his knife whenever he finishes his chain, to stab Big Blue. It is generally used to make a high damage critical strike on an opponent. After doing so, he starts his chain on another nearby enemy.
Slush Tile Rush
Marcstick's chains/attacks all involve his knife. Whenever his ultimate move is activated, there is a 15% chance that he could deal an amazing 300 damage attack with his knife.