PK Starstorm is the Final Smash of both Lucas and Ness in Super Smash Bros. Brawl. The character summons a rain of meteors from the sky while yelling "PK... Starstorm!!", which strike the stage. Lucas's PK Starstorm is more effective on smaller stages and Ness's PK Starstorm is more effective in larger stages. The move differs slightly for the two characters who use it; Lucas' meteors rain downwards in parallel lines, dealing 14% damage, whereas Ness's meteors spread out in a "fan-like" shape, dealing 20% damage. Lucas's PK Starstorm falls faster when he is on less damage, while Ness's PK Starstorm falls faster when he is on high damage, the damage each 'star' does could possibly be based on the user's damage as well. Ness's PK Starstorm knocks the opponent up while Lucas's knocks the opponent to the side.
Ness Trophy
Ness as he calls down a host of damage-dealing stars in his Final Smash. Everyone on the screen must dodge like crazy to avoid getting hurt, but that's no easy task. This attack appeared in the MOTHER series, but it was Poo, not Ness, who wielded it. Perhaps Poo taught Ness the secret of the attack for use in Super Smash Bros. Brawl.
Lucas Trophy
Lucas's Final Smash. He pulls a large group of stars from the sky and sends them smashing down among his enemies, causing damage to one and all. In MOTHER 3, this move was used by Lucas's traveling companion, Princess Kumatora. As Ness learned this move from Poo, Princess Kumatora taught Lucas when he learned he would appear in Super Smash Bros. Brawl.
Origin
Neither Lucas nor Ness actually learn PK Starstorm in their respective games. PK Starstorm is used by Poo (EarthBound) and Kumatora (MOTHER 3).