Mat too far up

The mat in the Pokemon League is up 1 space too far.

Surfing Music Before you Surf

If you have a bike on Select, you press select and then you keep tapping A on surfing water. The surfing music will be before you surf.

Missingno.

Missingno can be found randomly in the game.

Walk into Mewtwo

Thanks to kdogneo2 from Serebiiforums:

If you use an item when you're trying to catch Mewtwo or an item close to the time of having caught it. (Optional?)
Walk up to where Mewtwo was standing.
Save your game at the same place or back at the Pokecenter.
turn it back on and open your game file.
And watch the Plot Synopsis (The history reminder thingy) And you can see yourself move into Mewtwo! Mewtwo hasn't been taken out of the history thing. So you can see corners of your sprite behind Mewtwo!

Thunder/Thunderbolt Glitch

When Thunder/Thunderbolt is used in battle, sometimes that game will freeze and Thunder/Thunderbolts noise will stay there until you turn off the game.

Note: This may also happen with Ice Beam

Poisoned From Digletts Cave

When you leave digletts acve, you could be poinsoned

This is still not proven.

Transporting Runner
go to resort gorgeous. Beat the runner dude, then walk until your vs seeker is charged. be above the fence and one square right of the lady there. wait until he walks around to you. use the Vs. seeker. if he doesn't battle you re charge the seeker. try again until he wants to battle you. battle him and then after you beat him walk off the screen. walk back on and he will be one square up and he will continuously look in the direction you battled him in until you walk off of the route

pokedex Mssing Words
In the pokedex, under the entry, some pokemon have missing words. Heres a list of the words that should have other words after them: Aipom : long
Phanpy : long
Pidgey : tiny
Squirtle : tiny
Totodile : big
Primeape/mankey : pig

RUMOR: Poisoned Healed
Its rumored that there is a place in Viridian forest that when you walk by it any poisoned pokemon would be healed