How do you do the tweak glitch in Pokemon Diamond?

You can do it by going to Jublife City and going to the northern area of it.If you fail,your game may need to be restarted,so just in case,save before you attempt and have a Pokemon that knows fly.

Here's how to start,go to the top of Jublife City and go down using your bike in the fastest gear and just fidget with the left,right and down buttons;example:left,right,down,down,left,right,right,but fast.

If successful,you should be able to see a black inter-void and go in.You can get the following Pokemon by tweaking:Shaymin,Darkrai,Cresselia,Giratina,and Arceus.

P.s.if your game freezes,turn your game off and restart.

P.s.s.if you get stuck in endless darkness,fly to any city.