Question

I know that in the beginning of the battle it lowers the attack
but by how many stages does it lower it?
and if I switch out does it wear off?
when I switch out with another Pokemon, it doesn`t say that the intimidate cuts
the attack but does it?

Answer 1

By 1 stage.

Intimidate lower's the Attack of all opponents by one stage when the ability-bearer switches in (including the start of a battle). -Pokemon DB