Ok I know that it's a path in twist mt., but which one??? a map would really help.Edit: ok I meant reversal Mt.
You must go to the east of reversal mountain outside. This video will show you how.
Go east of reversal mountain.
See my other question: http://pokemondb.net/pokebase/117319/how-do-i-get-to-the-strange-house-white-2
there's no path in twist mountain, there is a path just before reversal moutain