The following year, Blackman joined Ken Shamrock in his efforts to combat the Nation of Domination. Eventually Blackman broke out on his own, establishing his trademark entrance involving swinging glow-in-the-dark eskirma sticks before walking to the ring. He eventually turned heel after siding with then-heel Shane McMahon. During his run as a heel, he brought a gym bag full of martial arts weapons with him to the ring, including kendo shinai. Blackman would attempt to use the weapons in the bag during or after the match. This was also during the time when he feuded with his former partner, Ken Shamrock. The two engaged in a heated feud throughout the summer, with it culminating in a Lions Den match at Summerslam 1999.
In late-1998, Blackman competed in the WWF Brawl for All tournament, defeating Marc Mero in the first round. However, he had to withdraw due to injury, allowing Mero to advance by default.
Blackman and Al Snow then formed a tag team that was known unofficially as Head Cheese, as Snow made Blackman wear a cheesehead hat to complement the mannequin head that Snow carried to the ring. Blackman had a reputation for being very serious and not displaying emotion, so the two put on comedy duo skits with Blackman as the straight-faced man. Many of the skits involved Snow's attempts to come up with a gimmick for their team. In one backstage scene, Snow proposed that the duo develop a TV show wherein they travel through time and solve mysteries. Another memorable sketch involved Snow scheduling an unsuspecting Blackman to perform stand-up comedy at a nursing home, with humorously disastrous results.
After the Head Cheese team went their separate ways, Blackman entered the WWF's Hardcore Division. At the time, the title was defended 24 hours a day, 7 days a week as established by Crash Holly. Because of this, WWF often ran matches wherein the champion was attacked and defeated in locations not typically associated with wrestling matches, such as backstage or in a hotel. With Blackman as champion, however, surprise attacks no longer resulted in title changes: within the matches, Blackman was so dangerous in hand-to-hand combat that surprise attacks were not effective enough to defeat him. During his stint as Hardcore Champion, Blackman's full martial arts talent was utilized. The first time he lost the title for a significant amount of time was against Shane McMahon, largely due to interference from Test, Albert, Edge, and Christian, with Mick Foley suspending the 24/7 rule to make sure McMahon didn't try to get out of facing Blackman in a rematch. At SummerSlam, Blackman fought McMahon for the title. During that match, they both climbed the TitanTron with Blackman able to knock Shane off with a Singapore cane, then performed a diving elbow drop for the pin fall . Blackman would go on to defend the title on several occasions, but he would ultimately lose the title on a more permanent basis to Raven in late 2000.
Early in 2001, Blackman formed another tag team, this time with Grandmaster Sexay. Blackman again played the straight-faced man: a recurring element was that Grandmaster would always try to convince Blackman to dance with him after their matches. In the summer of 2001, Lawler was released from his WWF contract. At around the same time, Blackman suffered an injury, and was released in October 2002.
On the March 29th 2013 episode of JBL & Cole Show, Blackman made a brief cameo appearance at the beginning where he made fun of JBL and Teddy Long.