There are plenty of options. Haze Toxapex / Clear Smog Amoonguss (watch out for SE Stored Power, though) Shadow Sneak, Sucker Punch, Unaware, or even Aqua Jet. A variety of Pokemon would work, like Aegislash, Azumarill, Cinderace, Clefable, etc. Polteageist also sometimes only carries Stored Power and Shadow Ball as it's attacking moves, using Strength Sap over Giga Drain, so Obstagoon is an unreliable counter to it. To be honest, you should be more scared of Focus Sash sets than White Herb ones especially without any priority.
Hope this helps! :)