Mr. Game & Watch: Oil Panic (down B)
With this move, I've dealt 117% in one hit, as well as KO at 0%. When a foe sends a powerful projectile in your direction (the best one would be Samus's fully charged shot), hit Down+B to catch it in the oil bucket. Do it two more times, and you can hit Down+B to scald your opponent in hot oil. The damage dealt is proportional to the power of the projectiles caught, hence the 117% I dealt.

Ness: PK Flash (B)
This move is kind of tricky to learn how to do well. Just hit B and hold it, and the green flashy stuff will slowly rise, then fall to the ground. You can control its direction with the Control Stick. You can release B at any point to detonate it, but to deal the most damage you should keep holding B until it detonates by itself.

Ganondorf: Tornado Kick (Smash Up+A)
This is hard to time, especially if you're charging it, but if you hit it just right and catch your victim in both upward foot swings, you can deal over 50% damage.

Ganondorf: Nightmare Lunge (Smash Forward+A)
This is a fairly simple move to pull off, and is among Ganondorf's quicker smashes. Nevertheless, it can pack quite a punch, especially if fully charged.

Ganondorf: Warlock Punch (B)
Arguably the most powerful punch in the game, not only does the Warlock Punch deal about 30% in a single hit, but it sends foes flying surprisingly far, dealing an easy KO at low damages.

Bowser: Hammer Head (Smash Forward +A)
This brute has a smash you shouldn't sneeze at: his Forward+A smash. Charge it up, and let 'er rip! It's slow, but will leave the victim needing more than a few stitches.

Donkey Kong: Giant Punch (B)
It takes a fairly large window of opportunity to fully charge this collosal attack, but it only takes minimal time to unleash on an unsuspecting opponent. It only takes a split second to miss it, though, so don't use it aimlessly.

Roy: Flare Blade (B)
This move is slow, but if it's pulled off it's an instant KO on all but the largest of arenas. Find a good time to hold the B button down for about 4 seconds, like when an opponent is asleep or attempting to recover back to the arena. The resulting attack creates a giant fireworks display that also damages Roy a bit.

Pichu: Skull Bash (Forward+B)
This baby Pokemon is a lot more powerful than his bigger brother Pikachu, probably because he hasn't learned to control his power yet. A fully charged Skull Bash is difficult to hit with, but in a 3 or 4 player melee, the window of opportunity is oh so big, and the damage dealt is insane - about 40%.

Yoshi: Flutter Kick (Aerial Down+A)
This is the infamous Home-Run Contest winning move. You can get about 40% off an opponent by jumping lightly towards them and holding down+A as long as you can. Yoshi's feet move fast!