The liquid nitrogen is an item present in Year 4. It is a small blue canister, which is recieved from Toto Santos. He uses it for lessening the pain of getting tattoos, even though it says "Do not use on bone."
Upon recieving the item, it is used to freeze Glottis' vomit to free the Bone Wagon from the explosive trap. Later, when Manny is shot by Hector LeMans, he uses it to freeze the sprout, and remove it, therefore saving his life. It has no further uses.