Buff

A buff is a term used to describe the improvement of a character (or aspect of a character), either through updating a game or by releasing a sequel.

From Brawl To Legend (Melee Characters Are Also Included)
Link: better jumps, significantly higher air speed, less falling speed, his aerial attacks no longer have high lag, significantly higher knockback in attacks, more power, significantly higher priority, faster running speed, Bombs have more power, Gale Boomerang now traps the opponent on the way back, brand new recovery, arrows can now be combined with bombs to make Bomb Arrorws, better chain grabs (now can chain grab every character with every throw). Link is the most significantly buffed character from Brawl to Legend.

Mewtwo: Heavier weight, more KO power, higher prority, Shadow Ball no longer causes recoil, better recovery, more knockback in attacks, more powerful throws, better chain grabbing ability, new side special, down smash now hits both sides, up throw has significantly higher power and knockback, faster character, better air game, faster walking and running speed, less floaty (making him less predictable). Mewtwo is the most significantly buffed character from Melee to Legend.

Samus: Regained her killing power from Melee, but with more power and knockback. Her dashing speed has been significantly increased. Faster air speed. Her d-tilt now meteor smashes if the opponent is hit at the top of the cannon, not the blast. Her jumps are now higher. Her bombs can now reliably kill as low as 90%. Her Missles has wider range and can kill at 100%. Her Charge Shot is significantly stronger, now capable of killing as low as 50%. Tied with Link for most significantly buffed character from Brawl to Legend.