It may sound very trivial, but when Zhin enters his counter stance, stop attacking him immediatly, or, if you play an area damage champion, try to aim for his back or sides!
Willo's Deadzone completely negates Grover's ultimate, so a good Grover will avoid using it while you're nearby. Use this knowledge to help your teammates corner and kill him, but be wary of flankers because you're first on their hit list.