 Nikishyn won a bronze medal in the team men's épée event at the 2006 World Fencing Championships in Turin, Italy, a silver medal in the team men's épée event at the 2013 World Fencing Championships in Budapest, Hungary, a gold medal in the team men's épée event at the 2015 World Fencing Championships in Moscow, Russia, a bronze medal in the individual men's épée event at the 2018 World Fencing Championships in Wuxi, China, and a silver medal in the team men's épée event at the 2019 World Fencing Championships in Budapest, Hungary.Nikishyn won a bronze medal in the individual men's épée event at the 2016 European Fencing Championships in Toruń, Poland, and a bronze medal in the individual men's épée event at the 2018 European Fencing Championships in Novi Sad, Serbia.Between 2006 and 2019, Nikishyn won two FIE Men's Épée Grand Prix titles, in addition to two silver medals and four bronze medals.