One day, the towns people couldn't take it anymore and devised a prank of their own and sent it to the queen (knowing that the queen had no sense of humor) and signed it from Jack. When the queen opened the gift from "Jack", she sent a knight out to kill him. The next day, the Grim Reaper went to reap his soul but Jack stole his scythe and would only give it back if Grim had granted him immortality. When the deal was done, as punishment, Grim decapitated him.
Later on, Jack got himself a pumpkin and wore it as his new head. He still lives in his old house untouched by time and every Halloween night, Jack emerges with a sack full of trick and plays terrible pranks on the people of Endsville.
Billy and Mandy's Jacked Up Halloween
While trick-or-treating, Billy runs into Jack's old house and goes there looking for candy. When Jack realizes Billy was carrying Grim's scythe, he tricks Billy into giving it to him and then brings demons from the Underworld to the surface world having them use pumpkins for bodies.
When Jack finds Grim, he plans on using the scythe to "return the favor" but Mandy tries to save Grim by devising pranks of her own only to be caught by Jack. Irwin instead is the victim of Mandy's pranks causing the possesed pumpkins to laugh themselves to death and Jack joining them all in the Underworld by a vortex but is still alive.