Heads, You Lose is a novella written by R. L. Stine. It was first published in 2010 and is the fifteenth book in the Goosebumps HorrorLand book series.
Jessica and Ryan can't wait to use the two-headed 'joke' coin they bought from the HorrorLand gift shop. But the joke is on them. One simple toss of this coin whisks them back in time, into a world of terror.