Zara Larsson BOSSED her Monster Mash-Up debut in London This image appears in the gallery:#MonsterMashUp 2016: ALL The Photos From Last Halloween's BIGGEST Party 25. Zara Larsson BOSSED her Monster Mash-Up debut in London (Pic: PA) 77 images See the full gallery: #MonsterMashUp 2016: ALL The Photos From Last Halloween's BIGGEST Party