Local singer-songwriter Taylor Swift tops the bill at Z100's glitzy holiday bacchanal. The undercard ain't too bad either: mini-Mariah Ariana Grande, Aussie pop-punks 5 Seconds of Summer, rising electro-pop singer Charli XCX and a host of other heavy-duty hit makers (Maroon 5, Jessie J, Iggy Azalea, Calvin Harris, Pharrell, OneRepublic, Rixton, Rita Ora, Shawn Mendes and Nick Jonas) round out this inevitable teen screamfest.