If you're talking about the guy blocking the path to Sunyshore city in diamond and pearl, you have to defeat Team Galactica at the top of the mountain, beat palkia, etc. After that the guy is gone.
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he is in victory road.
go to the Pokemon league. there is a room where a guy "checks" to see if you have all 8 badges. in that room, there are these 2 guys blocking two paths. the guy on the left is blocking mt.silver
you need the natonal pokedex
Defeat Team Galactic on Mt. Coronet.
You have to get all eight gym badges
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To move the guy blocking Mt. Silver , beat all 16 gyms and talk to Prof. Oak
No you cant
Go around. You have to get to Viridian City to make him move. after beating the elite 4, take the S.S. Anne (or whatever it's called) in Olivine to Kanto.
Yes, he is in that cave you see right above Cerulean city. The only problem is the guy blocking it is only going to move after you beat the Pokemon league.
he is in victory road.
go to the Pokemon league. there is a room where a guy "checks" to see if you have all 8 badges. in that room, there are these 2 guys blocking two paths. the guy on the left is blocking mt.silver
No one is blocking the way to the Lake of Rage. There is one person blocking the Gym and another blocking the way to route 44.
you need the natonal pokedex
The guy blocking the cave is Cyrus and he is in spear pillar after you meet him the first time but you need 7 badges to get to spear pillar
That guy isn't blocking the door. It is the entrance to the Eterna City entrance. The correct path can be found by going straight and rock climbing when you are outside, instead of taking the door to your right. Just retrace your steps and try again.