Tabitha Smith was raised in Roanoke, Virginia. Her parents divorced while she was still young and her father remarried. Her relationship with her parents was tumultuous at best, and further declined after her mutant powers manifested. Her friends (Sandman included) had already given Tabitha the nickname Boom-Boom, due to her 'highly explosive' personality. When her mutant power developed, she discovered she could create balls of explosive combustive energy. During a time of high social anxiety, distrust and fear over mutants, her parents were not pleased that their daughter would randomly destroy things with her time-bombs. Boom-Boom's father wasn't a well-educated man, and he tried to beat the mutant power out of her. She resented him for it and placed a small explosive into the tray of his TV dinner. The resultant explosion enraged her father, who beat her so severely that she decided to run away from home and tried to adopt the code name “Time Bomb”.
Boom-Boom used her power to detonate telephone booths and vending machines to collect small change. She used the money to buy a train ticket to New York where she hoped to find a secret mutant school. Boom-Boom was still homeless and wandered around the city until she was discovered by the Vanisher. He recruited her into his gang of teen aged street thieves, the Fallen Angels, where she relished the chance to use her time-bombs as a distraction while the others would pick pockets and steal purses. The Vanisher became lazy and reaped the benefits of all their hard work.
Tired of his lazy attitude she called in her friend, Sandman, who in turn called in the X-Factor who the public believed to be a human group of mutant hunters. The Vanisher soon disappeared when Iceman & Beast arrived dressed as mutant hunters. Instead of fighting the Vanisher, they found Boom-Boom who placed one of her time-bombs down the back of Iceman's shirt. They chased her around town until she reached a dead-end. Although she bluffed them with a non-exploding time-bomb, they scolded her and made her cry. She lamented of her broken family. Although she didn't really need much training to use her powers, Iceman & Beast took her back to X-Factor, later to the X Mansion to learn self-control and restraint of her powers.
Boom-Boom, Skids & Armor had been sent to Angel's old boarding school, but left in the middle of the night when a boy named Taki appeared in his flying car. He claimed that Artie & Leech had been kidnapped by demons and wanted their help to save them. Taki adapted his flying car to be powered by Boom-Boom's time-bombs, and soon they were on their way to battle legions of demons who had been unleashed from Limbo during the Inferno.
On route to Manhattan the kids stopped to 'borrow' refreshments and clothes from some local stores. While Taki paid for everything, Boom-Boom gave the team a stylish new make-over. However, Taki was kidnapped by Crotus and given to N'Astirh to create a machine which would enable the demon sorcerer to create faster & more complex spells. A giant portal above Times Square was held in place by tiny mutant babies at each point of an inverted pentagram. As the X-Terminators flew in Taki's adapted flying machines to save the babies, they were joined by the New Mutants. The two young teams swapped roles; the New Mutants went to save the babies, while the X-Terminators went to save Taki. Together with the New Mutants, they closed the portal to Limbo and restored normality to the streets of New York. Afterwards, Boom-Boom and Pixie teamed-up with the remaining New Mutants to help save Magik from her Darkchilde destiny.
When the New Mutants returned the infant Illyana Rasputin to her parents in Russia, Mirage & her Pegasus Brightwind were suddenly struck down by a mysterious disease. They rushed her back to New York where Ship recommended that they visit Doctor Strange. Boom-Boom objected to an implication that she was too immature to talk to Doctor Strange. However, the doctor couldn't see them as he was meant to be dead. She didn't believe Wong's claims and threw a time-bomb into the Sanctum Sanctorum, which was defused by the Doctor while hiding in the shadows. He observed how both Boom-Boom & Rictor were arguing, and he recognized how they were both particularly sensitive to the evil magic that was effecting Mirage.
As the New Mutants escaped they found Prince Hrimhari imprisoned in another cell. They quickly freed him, and fled Hela's fortress. However, they were soon divided into two teams. Boom-Boom was forced to travel Asgard with Warlock and Hrimhari. The wolf-prince was often frustrated by Boom-Boom's ignorance of Asgard, and she was quick to anger when he spoke to her as if she as dumb. However, they managed to effectively work together by using his lupine strength to hurl her time-bombs at aerial enemies.
They received advice from the Hildy, who told them to find Tiwaz the giant sorcerer who lived in the icy wastes. Boom-Boom was knocked unconscious during a brief fight with ice giants, so when she woke in the icy lair of Tiwas she mistook him for another ice giant. She threw a time-bomb at him, but he turned it into a living ice-statue of a fairy. Although Tiwaz was unable to join Boom-Boom's small team, he was kind and Boom-Boom liked him. She began to see a friendlier and magical side to Asgard, and gave Tiwaz a kiss goodbye. He sent them to the hive of Queen Ula. There Boom-Boom's team saved the Warriors Three from execution and recruited Queen Ula's swarm as an army to fight Hela. Boom-Boom, Hrimhari & Warlock led the combined forces of the Warriors Three, Queen Ula's swarm, Balder the Brave, and Karnilla's kingdom of living statues into battle. The other New Mutants stopped Moonstar from executing Odin while he slumbered in his Odinsleep. However, they soon left Asgard and returned to New York.
source: http://www.angelfire.com/comics/benriely/
http://marvel.wikia.com/Tabitha_Smith_%28Earth-616%29
http://www.comicvine.com/boom-boom/4005-2159/