psychic entity with "golem" ability, enabling him to construct animated rock bodies for himself, with superhuman strength, endurance, resistance to physical injury, and the power to explosively shatter back into loose debris, then reform on command
Santo was identified in New Mutants (2nd series) #8, and given a last name and codename in #10.
Rockslide was killed in X of Swords: Creation #1 by Summoner in Otherworld. Because of the location of his death, Rockslide's resurrection in X-Factor (4th series) #4 was corrupted, producing a new entity with an as-yet-ambiguous level of connection to the previous Rockslide. He was nicknamed "Wrongslide" by the mutants of Krakoa, as mentioned in X-Men: Red (2nd series) #4.