A short film prequel, 12 Begin (2006), was made as part of the film's pre-release promotional campaign. It was shown in limited screenings at SF Cinema City theaters. A sequel called 14 Beyond (2009 was released in Thailand in 2009.
The trivia item below may give away important plot points.
Phuchit's 13 tasks: 1. Kill a fly. 2. Swallow the fly. 3. Make three children cry. 4. Beat up a beggar and take his money. 5. Eat a plate of feces served to him in Chinese restaurant. 6. Give mobile phone to mentally unstable man at bus stop and then take another mobile phone from gang of youths on bus No. 6. 7. Retrieve man's corpse from well. 8. Beat ex-girlfriend Maew's new boyfriend with a chair. 9. Find old woman in hospital and escort her from the building while evading police. 10. String up wire clothesline across highway, which decapitates several motorcyclists. 11. Kill Tong or her dog (Phuchit kills the dog). 12. Slaughter cow and find a key in the intestines. 13. Kill John Adams (hooded man in wheelchair).