On September 22, 2017, at Death Before Dishonor XV, The Motor City Machine Guns defeated The Young Bucks to win the ROH World Tag Team Championship for the first time. They would retain the titles until March 9, 2018, when they lost them against The Briscoe Brothers at ROH 16th Anniversary Show. In June, Shelley suffered an injury. On July 20, 2018, it was reported his contract with ROH expired and left the promotion to focus on his wrestling school. Four days after, Shelley announced his retirement. On June 30, 2019, Shelley returned to ROH and announced he wants a match with the winner of Manhattan Mayhem, hinting that he might come out of retirement. On July 21, 2019, Shelley came out of retirement to team up with Jay Lethal and Jonathan Gresham to beat The Kingdom. On August 9, 2019, at Summer Supercard, Shelley was defeated by Matt Taven for the ROH World Championship. On December 13, 2019, At Final Battle, Shelley defeated Colt Cabana. On the January 1, 2020 episode of "NXT", the participants to the Dusty Rhodes Tag Team Classic were announced, with the exception of Kushida's partner, whose identity was kept a mystery. On January 8, a surprise announcement was made that Shelley was coming to WWE, as part of the NXT brand and would be Kushida's partner, reforming their Time Splitters tag team for the first time since their New Japan Pro Wrestling days in 2015; this is Shelley's first time performing on WWE, after a one-off appearance on "WWE Heat" back in his early wrestling days in 2005. On the January 15 episode of "NXT", Shelley and Kushida lost to Grizzled Young Veterans (James Drake and Zack Gibson) in the first round of the tournament. Shelley has appeared in the video games "TNA Impact!" and "TNA Wrestling Impact!". Martin is a fan of punk rock. He has worn the logo of the band Teenage Bottlerocket on his ring attire and the band has talked about being in contact with him.