“It: Welcome to Derry ” costume designer Luis Sequeira had previously created the wet, bloody look for “Carrie,” so he already understood what it would take to recreate it for Stephen King’s killer demon clown. Or at least he thought he did. Having worked on the film “It: Chapter Two,” he was already familiar with the universe. In the season finale of “Welcome to Derry,” Pennywise (Bill Skarsgård) is seen hibernating in human remains, soaking in blood. The unnerving image, however, is of him emerging in all his bloody glory in a red outfit. To retain that visual storytelling element, Sequeira needed to show wear, tear, and patina. “If you literally wet something, you lose that patina. It’s just dark,” he told Variety. Popular on Variety Here, he breaks down the process behind the red outfit look, and creating Periwinkle’s clown look and inserting easter eggs that nod to Pennywise’s universe.…