pretty simple use these steps to beat them
A.The Lucky Shot
lets say you are using a diagla on your team give it the ring target (moves hit regardless of abilities) then use roar of time and hope for the best
B. The toxic The Shuckle And the Sandstorm
pretty simple shuckle uses toxic (holding ring target) and just stall sandstorm would add extra damage
C. The return of the Mummy
Configaruis enough said
D.How learn to a new skill to swap
uses manaphy's skill swap (holding ring target) and now manaphy has wonderguard
E.Who broke the mold?
Use haxorus with molder breaker and just wail on the opposer

Of course if you actually face a wonderguard spiritomb who care if they beat you? they won by cheating/pokesav.

Um.... wut?

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i know but so many people complain about this thing

Only Shedinja possesses this ability? Or is it a dreamworld ability? Doesn't matter for me, I have numerous moves super effective against that spinny thing.

its a common hacked pokemon

Added after 37 minutes:

also recently discoverd zekrom and reshiram are also good

Spiritomb or wondertomb as hackers call it has no weaknesses and since wonder guard only allows super effective hits you can't hurt it with a normal attack.

Also cranidos and rampardos work because they have mold breaker. Also a lot more pokemon can learn skill swap but skill swap will not work on wonderguard. Another tactic is soak turning it into a water type. Lastly mummy will not work wonder guard and multitype resist it. Oh and you don't need the ring target for those moves. (first off ring target harms you if you are holding it. It alows moves that would have no effect on you hurt you. Such as normal/fighting on ghost electric on ground etc. So that doesn't mean anything unless you trick it over. Also it's Co***rigus not cofigrigus).

Edit: also there is wondereye which is sableye with wonder guard (same type dark/ghost giving it no weaknesses either) Also you can use odor sleuth, foresight, or have the ability scrappy and use fighting moves.

what about the fire fang glitch?

That works for 4th gen but it was fixed (how can you fix something that would never have been noticed without hackers -.-) in 5th gen

i think nintendo is making a secert pokemon team to go out and beat up hackers