Rokk Krinn (Cosmic Boy)

Rokk Krinn is a member of the Legion of Super-Heroes from the 31st century under the name Cosmic Boy. He and two other members of the Legion returned to the past to help Clark defeat Brainiac.

Cosmic Boy's Powers

 * Magnetokesis: Rokk can manipulate and control metal objects just by thinking. He seems to have fully mastered this ability, as he was able to summon the Persuader's Atomic Axe from his hands to his own with ease and was able to carefully extract all of Brainiac's nanites out of Chloe Sullivan via her mouth without removing her other need nutrient trace metals. He was also able to use his own powers together with Garth's to create an electromagnetic pulse that temporarily took Brainiac offline.
 * Flight: When Rokk wears the Legion of Super Heroes ring, he is gifted with the ability to soar through the air. The ring does the same for the others who wear it.

Weaknesses
Rokk Krinn has no "clear" weaknesses, but Cosmic Boy's power cannot affect non-metals, such as organic substances like wood.

Season 8
Along with fellow founding Legion members Garth Ranzz and Imra Ardeen, Rokk traveled through time back to the 21st century to stop the Persuader from killing Kal-El aka Clark Kent and altering history. They found him to at Clark's barn where he had just returned from seeing Jimmy off to Star City. After the Persuader cut his abdomen, Rokk took away his atomic axe using his ability of magnetism and Imra distracted him using telepathy enough so that Garth could knock him out using his electricity. Once unconscious, Rokk took away the Persuader's stolen Legion ring, sending him back to the 31st century to be contained. Rokk, Garth and Imra then introduced themselves to Clark as the Legion of Super-Heroes. The three explained to Clark what he is truly destined to be, which is a model for all of the galaxy for aliens to come to earth and live among humans. Rokk learned that the Persuader did not just come to kill Kal-El, but to destroy the Phantom Zone Crystal, the Martian Crystal belonging to Martian Manhunter, to prevent the destruction of Brainiac and thus destroying the future since that was how Clark defeated Brainiac in the future.

The three Legion members decided to help Clark defeat Brainiac since history is different now and they were willing to stop Brainiac at all costs even if it meant killing its human host: Chloe Sullivan.Clark initially refused their help since they're willing to kill a human being to stop Brainiac. After managing to stun Brainiac as it was trying to drain knowledge from the human race through computers, Garth tried to take on the responsibility to stop Brainiac, but Rokk wanted to do it instead, seeing that Garth was not up to murdering someone.

Finally working together after Clark stopped Rokk's attempt at killing Chloe/Brainiac, Clark and Imra were holding Brainiac down and making contact with Chloe from within, while Rokk and Garth managed to electrically and magnetically extract the nanites of Brainiac from her. As they did, the particles had formed a sphere and disabled Brainiac for good. Rokk, Garth, as well as and Imra returned to the future with what was left of Brainiac to be reprogrammed into something useful, but not before Rokk warned Clark to be careful of the days ahead.

Returning from the future to the 21st century once again, Rokk goes to the Daily Planet rooftop to meet Clark and told him that by saving Chloe from Brainiac, he saved her connection to Doomsday and that Chloe is the reason that Doomsday cannot be defeated now since she made him immune to kryptonite when she tried to kill him with it and she stopped Clark from sending Doomsday to the Phantom Zone at the Fortress of Solitude with the Black crystal.

Clark states that he wouldn't change his decision on saving Chloe no matter what happened and then Rokk tells Clark that tomorrow is the day he'll die if he goes up against Doomsday head-on. He gives Clark another Legion ring since his old one got destroyed a while ago and suggests that Clark send Doomsday to the future to fight The Legion since nothing on the planet can stop him from killing Clark, then he returns to the future when Clark refuses to accept his help, stating that this is his problem, not the Legion's and that he will embrace his destiny, even if it means that he'll have to die to do it. Rokk's meeting fulfilled its purpose as his warning prompted Clark to create a plan to imprison Doomsday beneath the surface of the Earth rather than face him in a head-on battle.