The jack lantern mask was one of two rewards from the 2006 Hallowe'en event. It has no bonuses and is purely cosmetic. Diango, located in Draynor Village, will return the mask to any player who has lost theirs. This is a discontinued item.
Similar to the skeleton costume, it is very uncommon to see other players wearing the jack lantern mask around RuneScape. Players consider this item to be rare. It is sometimes mistaken for the Pumpkin, which was the first ever event item, and is also discontinued.
During the 2010 Hallowe'en event, wearing a Jack lantern mask whilst talking to Pumpkin Pete will give an extra dialogue saying "What-ho! Now there's a good looking chap!". When speaking to Pumpkin Pete wearing the mask during the event, he may add small phrases like "Still looking good, I see."