1) pick Fox as your own character and a slow opponent (lv9 but i think it also works when playing against a level 1)
2) select the kongo jungle stage (the one with the rock at the right side of the stage)
3) lure your opponent to the rock at the right side of the level and quickly jump back to the edge of lowest part of the wooden platforms (your opponent has to stay on the rock) and keep shooting (B-neutral) in your opponent's direction
4) it will jump to you and airdodge in the air between the rock and the wooden platform
5) KO!
another one: (this one's not really a glitch i think)
1) pick fox (or falco) in training mode (it doesn't matter who your opponent is)
2) choose a red shell from the item menu to appear in front of you (not more than 1)
3) use reflector so the red shell will keep moving and hitting your reflector
4) after the red shell hit your reflector about 5-6 times, your reflector will BREAK!
5) each time your get hit by the red shell after your reflector broke your recieve an amazing

amount of damage: about 72% per hit
6) if you want to get 999% of damage, you should try this and repeat it a several times (because the red shell will never KO you)
3rd glitch:
1) pick a random character (doesn't matter who) and pick Ness as your opponent (lv9!)
2) pick the jungle japes stage (the one with Cranky in a house)
3) do nothing
4) Ness will kill himself as he's trying to get to you.
5) another (wonderful

) KO
but as G-regulator said, it will work with Fox as your opponent too (and maybe with even more characters)
another:
1) pick sheik as your opponent
2) go to kongo jungle (the one with the rock)
3) get sheik to the rock
4) he will sometimes (it doesn't always work) just walk of the rock at the left side and jump back on, and he will keep repeating this until you come near him or hit him with an attack
more:
1) pick fox as your opponent
2) choose hyrule temple
3) get fox to the little platform under the stage (a white-colored platform)
4) get away as quickly as you can
5) fox will come after you but keeps repeating this (this doesn't always work): walk off the platform at the left side, use fire fox to get up the stage (not the platform), walk to the part of the stage under the middle, jump until he hits the ceiling, walk back to the white platform, then he'll fall into the space between the platform and the stage again and comes back with fire fox again, and keaps repeating this forever if you don't hit him with an attack. (if I remembered correctly, it was this what he did, but i'm not sure of it)
Hope you enjoy 'em
