This being Saudi Arabia, where strategic ambiguity reigns as social changes sweep across the country, the government-sponsored event was not, strictly speaking, a Halloween festival. Like many of those swarming the entertainment complex on Thursday night — jamming the surrounding neighborhood into gridlock and making any search for parking in vain — the al-Hazzazi cousins wanted costumes that would attract attention. They threw together their makeshift mummy outfits using medical gauze they bought at a pharmacy and improvised fake blood using Vimto, a sugary red drink consumed during Ramadan, the Islamic holy month.