Become a goast pokemon, use a mobile orb or get the IQ skill super mobile.
You can also use a mobile scarf.
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The mobile scarff allows you to walk through walls but it makes your belly go down FAST!
I don't think there is one, but if your Pokemon has maxed out IQ, they'll have the Super Mobile IQ which lets them smash through walls, if that's what you meant.
The walk through walls Gameshark code for Pokemon Red is 010138CD
do what is the walkthrough walls action replay code for Pokemon heartgold.
Action Replay