It really depends on what type he is. Just try to use type advantages as much as possible. He is only in the Uber tier (obviously) so you will only face him when you have some pretty powerful Pokemon of your own. There is no solid counter to him, as he can be any type at all, so something that will resist whatever type of Judgement he will use, and can do super-effective damage to him is preferable. He will often use Thunderbolt and Ice Beam as well, so something not weak to that is also a bonus. If you can, scout out what moves he has in particular, as he does have a very diverse move set, but I think Ice Beam + Thunderbolt + Judgement is pretty standard on a Special Attacker set. Occasionally you may find a physical attacker, but I don't think they are as common.