A mod pack I've been slowly working on for about two weeks now, I plan to have every character changed in their own unique ways, with the exception of a few characters that can't be modified. Warning: It's best not to play with Items, otherwise certain fighters (namely Peach) glitch in weird ways when they hold one.
So far, after working off and on, I've completed 4 fighters: Mario, Luigi, Peach, and Captain Falcon.
Mod Changes:
Mario: His Up-Tilt, Down-Tilt, F-Smash, Nair, and Grab have had their damage increased heavily, at the cost of making him take self-damage; the Cape similarly deals self damage in exchange for sending Mario high up into the air (Equivalent height of Up-B); FLUDD now hurts him while charging up, but the water now deals damage as well as knockback; when his shield gets hit, he and the opponent who attacked him take a small amount of damage.
Luigi: His Dash-Attack and Down-B are much more powerful; Side-B does more damage and goes farther but it charges slower and can't misfire; Up-B's direct shot is less powerful, but the small hit does roughly the same damage; Neutral-B now fires three fireballs that do less damage.
Peach: Side-B, Grab, and Down-Throw do less damage but heal her in return; Down-B no longer generates a Turnip, instead healing her a small amount on demand; Up-B goes higher but falls much quicker (faster than her normal falling speed); her Final Smash no longer deals damage. (Glitch warning: For some reason she can't pick up the peaches that spawn when she uses the final smash.)
Captain Falcon: Slows down time when Dodging, using Up, Side, or Neutral-B, taunting, after his Shield is damaged, or charging any smash attack.
Other Info: There are no visual changes in this mod, at least so far, so there aren't any screenshots I could put as previews.