It reverses the stat changes, so it would drop it two stages. It wouldn't work the other way around, that is, the pokemon with the ability perversity uses it against a pokemon and said pokemon loses attack and becomes confused.
"All moves or abilities that would normally increase a stat will decrease it, and ones that would normally decrease a stat will increase it. This also applies to self-inflicted moves, such as Charge Beam, Close Combat and Leaf Storm. This does not include Baton Passed stats."