Damián 666, Halloween and X-Fly hand Los Psycho Circus their first-ever loss in a steel cage weapons match. On March 18, 2011, at Rey de Reyes, Aguayo Jr. joined Damián 666, Halloween and Super Crazy in a winning effort against Potencia Mundial (Dr. Wagner Jr. and Los Psycho Circus); Aguayo Jr. pinned Wagner with La Lanza, following a chair shot. On April 8, 2011. Aguayo Jr. underwent emergency surgery to remove a golf ball-sized tumor from his stomach. During the surgery, a peptic ulcer burst, and he was placed in an intensive care unit at the hospital in Guadalajara, Jalisco. Aguayo Jr. was released from the hospital on April 19 and was scheduled to receive treatment for his condition for a full year. Aguayo's tumor was found to be benign; Aguayo made his return to AAA, in a non–wrestling role, on May 1 and returned to the ring on May 8 in a six-man tag team match pitting Los Perros del Mal against Los Psycho Circus; Aguayo pinned Psycho Clown after a low blow. The feud continued on May 29 at Perros del Mal Producciones' third anniversary show, when Los Psycho Circus defeated Los Perros del Mal in a six-man tag team steel cage mask vs. hair match. As a result, Super Crazy, the last man left in the cage, was shaved bald. Aguayo Jr. was set to wrestle as part of Los Perros del Mal at Triplemanía XIX, facing Los Psycho Circus to determine the first-ever AAA World Trios Champions, but was forced to pull out of the event due to an adverse reaction to the medication given to him as part of his tumor treatment. Aguayo returned on July 24 at a Perros del Mal event, teaming with Damián 666 and Halloween against Blue Demon Jr., Cassandro and L.A. Park; the match ended in a no contest when Park turned on his partners. Aguayo Jr. next returned to AAA on August 19, replacing L.A. Park and teaming with Damián 666 and Halloween against El Mesías, Joe Líder and El Zorro in a six-man tag team match, which they lost via disqualification when Líder was attacked by his former tag team partner Nicho el Millonario. After the match, Aguayo officially named Nicho the newest member of Los Perros del Mal. Aguayo Jr. returned to pay-per-view on October 9, 2011 at Héroes Inmortales, unsuccessfully challenging Dr. Wagner Jr. for the