There are multiple places with cops that won't let you pass. The most common place is in the Victory Road entrance, where you'll need at least 8 badges. If you want to go left, you'll need to have 16 badges.
you have to have rotom
In Goldenrod City, there is no cop guarding the radio tower. In Lavender Town, it is impossible to get past the cop. You do not even need to get past that cop.
Never
brain
Act normal
just use the rocks!
go over the gate
there is no 9th gym
first you must deffeat clair
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You cannot get past the cop at the Lavender Town radio tower. The guard is always going to be standing in front of the elevator. The cop tells you that the increase in criminal activity in radio towers prompted him to guard the elevator.
there is only a hoho, omynite, areodactly, and charzard