Crosta is an Atlantean that developed a mutantion that allowed him to create sonic booms. He was also disfigured because of this mutation.
Crosta was created to show Namors strength and leadership during Namors tenure in the Cabal.
Once a regular Atlantean his powers would manifest after his parents seperation. His mother and him went into hiding and he became close enough to his mother that when Namor tried to seperate the two, Crosta blasted Namor in defiance.
Major Story Arcs
Crosta's parents had gotten a divorce when he was very young. His father wanted to raise their child to be a soldier, while his mother wanted a different life for her son. Eventually (presumably at puberty), he developed a mutation that not only altered his physical appearance, but also gifted him with the ability to induce shock waves. When Atlanteans were ordered to take up life on land, the young mutant's mother remained undersea with her son, against Namor's wishes, feeling that her son would never know freedom on land.
Later, Crosta's father took his ex-wife to court, demanding custody of his son; he cited her disobedience of Namor as endangerment. Namor, however, decided that Crosta would join the X-Men and took the boy in himself. Upon learning of this, Crosta was furious, and attacked Namor, who stopped him with ease.
When Utopia was starting to sink back into the ocean, Magneto asked Namor for help in keeping it afloat. Namor had the Atlanians that were now in the area to build a pillar underneath the "Island" to keep it aflaot. When the X-Club heard about this, they went to see what was happening, they had no ideas how to keep the island afloat and going back to the mainland wasn't an option after the X-Men's battle with the Dark X-Men and Dark Avengers. Crosta is the one that greets the X-Club and goes to Namor.
Crosta seems to have the power to cerate sonic booms. It is unclear if he would still have his powers while on land.