 In the 79th minute he was replaced in instead of Akseli Pelvas, in the match Falkenbergs FF lost 0–2 to IFK Göteborg.On July 17, 2016 Karlsson made his first two Allsvenskan goals in a 3–3 match against Hammarby IF.He transferred from Falkenbergs FF to Swedish top flight IF Elfsborg on 2 December 2016, after a breakthrough season scoring 7 goals and 2 assists as an 18-year old.