Born in Thessaloniki, Mystakidis started his career in Germany playing for Fußball-Regionalliga Südwest club Freiburg II. In his actually first professional season with Pierikos, he worked very hard and his improvement is obvious. Mystakidis since his beginning in professional football, characterized as a talent with shoots, crosses and passes equally well with both feet. It can cover all three positions behind the forward is not predictable in his playing and has good finishes in both short and long distance. Mystakidis scores his first goal for PAOK on an unofficial match against Dnipro. On 16 July 2015 he made his debut with PAOK in an away loss game against Lokomotiva Zagreb for the second qualifying round of the UEFA Europa League. He scored his first goal in 2015–16 season in a 3–1 away win against Kalloni. On 25 August 2016, PAOK extended the contract of the young striker till the summer 2020. On 29 January 2017, he scored the only goal in a 1–0 Superleague Greece away win against Panetolikos. Two days later scored another goal in a 2–0 away win against AEL and a week after he scored 2–1 Greek Cup away win against Xanthi On 14 February 2017, it seems that talented winger of PAOK will be called up in Greece National Team very soon, after his recent impressive performances, as the German manager Michael Skibbe is watching closely the progress of 22-year-old player. The 2016–17 season was an establishment year for the young striker, as he had gradually managed to gain the trust of Vladimir Ivić. On April 2, in the 80th minute of the match against AEL for the 26th day of the Superleague Greece, the 23-year-old ace was forced to request an immediate change after an attempt to avert a throw-out. A day later, Mystakidis had a surgery, faced a cruciate ligament rupture that probably kept him out of the team for 6 months. On 19 December 2017, PAOK midfielder finally made his long awaited return to competitive football, coming on in the 82nd minute during the club's 5–1 Greek Cup away win against Trikala. It was his first appearance marred by a knee injury. He almost scored too, as a firm header was turned aside by the Trikala goalkeeper. Mystakidis received a nasty cut to the right eyebrow after a collision with an opposing player, but he brushed off the knock with minimal fuss. On 31 January 2018, he signed a six-months contract with rivals Panathinaikoson loan from PAOK, until the end of the 2017–18 season without a purchase option. On 20 August 2018, he signed a long season contract with PAS Giannina on loan from PAOK, until the end of the 2018–19 season without a purchase option. The loan contract was terminated on 4 January 2019, six months before it expires. On 2 February 2019, he joined Polish clubGórnik Zabrze on a six months loan from PAOK. On 30 June 2019, it was confirmed that Mystakidis would spend the 2019–20 season on loan at Volos. On 14 January 2020, it was confirmed, that he signed a contract with Eerste Divisie club De Graafschap until July 2020. The Greek attacker already traveled with the selection to the training camp in Spain. Both De Graafschap and Mystakidis looked back on a successful training week, after which all formalities were completed this week.
