On August 31, 2020, it was reported that Gacy had signed a contract with WWE. On the July 2, 2021 episode of 205 Live, Gacy made his television debut, defeating Desmond Troy to qualify for the 2021 NXT Breakout Tournament. On the August 3 episode of NXT, Gacy was eliminated in the first round by Trey Baxter. On the September 21 episode of NXT, Gacy began a new gimmick, portraying a politically correct spokesperson. He was later defeated by Cameron Grimes. On the October 5 episode of NXT, he defeated Ikemen Jiro and proceeded to give him a hug afterwards. The following week, he fought Tommaso Ciampa in a match where had he won, he would've been added to the NXT Championship match between Ciampa and Bron Breakker at NXT Halloween Havoc, but he was unsuccessful. On the November 23 episode of NXT 2.0, he convinced Cruiserweight Champion Roderick Strong to grant him a match for the title at NXT WarGames, despite not weighing 205 pounds or below. The following week, he welcomed everybody to his All-Inclusive Invitational, an open challenge for people of all shapes, sizes and genders, but was interrupted by Roderick Strong and Diamond Mine, who attacked him. At WarGames, Gacy was unsuccessful at capturing the title.
In April 2022, Gacy began feuding with the NXT Champion Bron Breakker after he and Harland kidnapped Breakker's father, Rick Steiner. Gacy's character began to morph into a dark and sadistic cult-like leader, who demanded Steiner's Hall of Fame ring in exchange for his safe return. A title match between Gacy and Breakker was later made official for NXT Spring Breakin'. On April 29, Harland was released from his WWE contract, thus ending his and Gacy's partnership. At Spring Breakin', Gacy was ultimately unsuccessful in capturing the NXT Championship. After the match, Bron Breakker would be attacked and carried out of the arena by druids. These druids would accompany Gacy and would sometimes attack Breakker. Gacy eventually challenged Breakker for a rematch at NXT In Your House, with the stipulation that if Breakker was disqualified, he would lose the NXT Championship; Gacy would fail to capture the championship yet again.
On the July 19 episode of NXT 2.0, Gacy revealed the druids' identities as the Dyad, consisting of Jagger Reed and Rip Fowler, formerly known as the Grizzled Young Veterans. Collectively, Gacy and the Dyad became known as the Schism, and they began a feud with Cameron Grimes. During this rivalry, the debuting Ava Raine would join Schism and cost Grimes in his final match with Gacy on the November 8 episode of NXT, ending the feud. Gacy competed in the men's Iron Survivor Challenge match at NXT Deadline in December, but was unsuccessful in becoming number one contender.
The Schism would slowly begin to disband in September 2023, beginning with The Dyad leaving the company on September 14, and culminating in a backstage segment during NXT No Mercy, where Gacy declared the Schism to be "dead".
During the second week of NXT Halloween Havoc on October 31, Gacy appeared in a vignette hinting at a new character change. Over the following weeks, he would appear in segments which included him appearing out of a car trunk and posing as a construction worker. On the January 16, 2024 episode of NXT, Gacy was part of the commentary tea, providing color commentary alongside Booker T and Vic Joseph during the match between Dijak and Trey Bearhill. Following the match, Gacy attacked Dijak, turning face and starting a feud with Dijak in the process. Gacy was defeated by Dijak in no disqualification match at NXT Vengeance Day and again at NXT Roadblock in an Asylum match. At Stand and Deliver, Gacy was attacked by Ridge Holland with a chair, but Gacy told the referee he was still able to compete. Gacy would go on to defeat Shawn Spears.
Gacy quietly moved to the Raw brand on the June 17, 2024 episode of Raw as a member of the Wyatt Sicks. Gacy would sport a pig mask, resembling Huskus the Pig Boy from Bray Wyatt's Firefly Funhouse.