Mondo was once friends with Cordelia Frost, Emma Frost's younger sister. In an attempt to make a bid for the position of White Queen of the Hellfire Club, Cordelia had Mondo contained and handed him over to the Inner Circle of the Hellfire Club. Cordelia's scheme backfired; the Hellfire Club kept Mondo but denied Cordelia membership. Cordelia went to Emma, headmistress of the Massachusetts Academy, for help and, soon after, Mondo was rescued by Generation X and subsequently accepted an invitation to join the school.
However, Generation X later learned that the Mondo they had rescued wasn't the real Mondo but a clone, a plant-based simulacrum created by Black Tom Cassidy who had infiltrated the Hellfire Club and rescued Mondo. After taking Mondo under his wing, Black Tom created a clone of the young mutant to infiltrate the Massachusetts Academy so that Black Tom could exact vengeance on his cousin, Banshee, who was the headmaster of the Academy. Years ago, Black Tom had raised and used Banshee's daughter, Siryn, in his crimes. Once the father and daughter met, though, the girl mended her ways. Black Tom has always blamed Banshee for taking Siryn away from him and now he planned to do the same with Banshee's students.
As Banshee and Emma Frost did battle with Black Tom, the Mondo clone began hunting down the members of Generation X. As the Mondo clone was about to attack Jubilee, however, it was shot dead by the anti-mutant militant Bastion, chief operative of Operation: Zero Tolerance.
Later, the real Mondo appeared alongside Black Tom and Juggernaut. Completely loyal to Black Tom, the real Mondo battled the members of Generation X. Generation X attempted to talk to Mondo into not fighting, but Mondo laughed at them, reminding them that he has never met them before. Generation X and their teachers were able to defeat their opponents, but the trio still managed to escape.
Mondo was not among the latest incarnation of the Brotherhood of Evil Mutants of which Black Tom was a member.