One quick correction Mr. Developer, the Froslass has Mold Breaker so it ignores Wind Rider and also Ghastly's Levitate for when it uses Earth Power. But frankly I found a pretty easy counter in anyone that can tank Special Attacks and spamming Calm Mind and then using Stored Power. The given Drowsee kinda goes crazy since it's not weak to any attacks and can learn both. Misdreavus as well but Shadow Ball might be scary, I forget if that's actually super effective for Possession type. Super consistent strat and Sheer Cold is just a quick reset.