Throughout the '90s and into the 2000s Warren produced several Dirty Pair comics and trade paperbacks, a four-part "Bubblegum Crisis" series called "Grand Mal" as well as cover, pin-up and other "freelance" art. During this time he provided numerous cover illustrations, most notably covers for the "X-Men", "Star Wars", "Fantastic Four" (while he was also penning a few stories), and "Appleseed" series, as well as some trading card art, and even in-house Christmas cards for Studio Proteus. Between Dirty Pair works he also penned a three-part Terminator series called "Hunters and Killers" in 1992. Towards the end of the '90s and into the early 2000s he was one of the main writers, and to a lesser extent artist, for the "Gen¹³" series from Wildstorm comics. He has done art commission work for "Spin Magazine" and "PSM " magazine. His PlayStation comics usually relate to their major featured article and are found on the back page of the magazine. His art has also been featured in their swimsuit edition. He has also been known to do some translation and scripting work, "Seraphic Feather" and "Cannon God Exaxxion" being two of the only known credited examples.