I dont agree with that, it says switch the defending pokemon So you get to choose, Now If unown G was already attached to a pokemon it cant be affected by special conditions, But you can't attach unown G to a pokemon that is already affected by a special condition. So the player playing frostlass would pick a pokemon without Unown G.2nd, kind of good, but since Unown G is up, not so good.
7.5/10 if no Unown G
4/10 w/ Unown G