The Jack O'Lantern is a tall man with a carved pumpkin for a head. He wears a 18th century gentleman's coat with a frilled cravat suggesting he originated from that time period and mainly attacks by spewing fire breath at his victims. It is believed that he's summoned when the three small jack o' lantern candles that are seen in the basement are lit.
The Jack O'Lantern is let loose from his cell during the Purge. One of the video monitors shows him burning people with fire breath. In the Official Visual Companion however, he appears in the second wave of the Purge, hinting that he was supposed to appear in the second wave, but was replaced with the Alien Beast.
The Jack O'Lantern was possibly inspired by characters from urban legends and ghostly folklore from Colonial-era New England, particularly those told during Halloween. One likely inspiration is the Headless Horseman from Washington Irving's short story, "The Legend of Sleepy Hollow" who, in many interpretations, carried a jack o'lantern for a head. In appearance, he also resembles the characters of R.L. Stine's Goosebumps: Attack of the Jack-O'-Lanterns. Additionally, he could be a rather literal reference to special effects master Stan Winston's directorial debut film, Pumpkinhead.