Achterberg faced Rinus Douma for the vacant Big Game -95 kg title at Big Game 2 on March 13, 2018. He captured the vacant title by unanimous decision. Achterberg next faced Baran Er at Fair FC 8 on October 6, 2018. He won the fight by unanimous decision. Achterberg faced Ali Boutaleb at Knock Out 2018 on November 24, 2018. Boutaleb retired from the bout at the end of the first round, after being dropped with an uppercut, which the referee failed to call. Actherberg faced Feliciano Weiß at Big Game 3 on March 23, 2019. He won the fight by unanimous decision. Achterberg was next booked to face Cedric Lushima, a mixed martial artist, at Ultimate Sparta Championship on April 13, 2019. He won the fight by unanimous decision. Achterberg faced Kevin Heerschlag at Fair FC 9 on October 5, 2019. He won the fight by second-round knockout, flooring Heerschlag with a head kick which left him unable to rise from the canvas. A month later, on November 23, Achterberg faced Ahmed Shah Ghazikhnani in a non-title bout. He won the bout by unanimous decision. Achterberg faxed Sandro Zulčić for the vacant Fair FC light heavyweight at Fair FC 10 on October 4, 2020. He won the fight by a second-round knockout. Achterberg made his
Enfusion debut against Peter Verhaegh at Enfusion 103 on October 23, 2021. He won the fight by unanimous decision. Achterberg faced took part in a 16-man tournament, held at Gladiator Fight Night IV on May 7, 2022. Achterberg won the quarterfinals bout of the tournament against Yankuba Fatajo by a second-round technical knockout, stopping his opponent with a flurry of punches at the very last second of the round. Achterberg faced Rafael Hering in the semifinals and won the fight by unanimous decision. This proved to be his toughest fight of the night, as he was able to cleanly knock out Jolton Peregino with a left hook in the second round of the finals. Achterberg faced Anthony Leroy in his SENSHI debut at SENSHI 13 on September 10, 2022. He won the fight by a first-round knockout, stopping Leroy with a flying knee. Achterberg faced
Jimmy Livinus at Senshi 19 on November 25, 2023. He lost the fight by a third-round knockout. On March 29, 2024, Achterberg announced he had successfully undergone cruciate ligament repair surgery. Achterberg faced the 2022 K-1 World GP Japan Openweight Tournament Winner
Mahmoud Sattari in the quarterfinals of the 2026 K-1 Cruiserweight World Grand Prix at
K-1 World GP 2026 - 90kg World Championship Tournament on February 8, 2026. He needed just 51 seconds to stop his opponent. Achterberg advanced to the semifinals of the one-day tournament, where he faced
Bogdan Stoica. He stopped Stoica midway through the opening round. Achterberg faced the Fair Fight Heavyweight champion
Nikita Kozlov in the tournament finals. He won the fight by a first-round knockout. ==Championships and accomplishments==