“Cellphone horror” updates itself as technology improves and its place in culture changes. In 2019, “Countdown” warned of the perils of downloading every newfangled popular app for funsies, especially apps that kill. This year, Jacob Chase’s “Come Play,” adapted from his 2018 short “Larry,” moves from phones to smart devices and cries “stranger danger,” reminding audiences that none of us know who’s watching us through our screens, or what; a pervert named Larry, perhaps, or an extra-dimensional child-snatching monster? Either way, it’s up to parents to keep their kids safe from skeezy weirdos and creepypasta bugbears on the Internet by limiting tablet time.