This is The Mature Gohan here throwing in my
  strategy for this very useful card we call Charity. Here is the card.
   
  Charity
  Attach Charity to your Active Pokémon.  Unless that Pokémon gets
  knocked out,return Charity to your hand at the end of your turn.  If that
  Pokémon attacks and does damage to the Defending Pokémon, you may reduce
  that Damage by any amount (rounded to the nearest 10).
   
  Most people will think it can be used just for Mr.
  Mime but can be used in another different way too. One is for Team
  Rockets Hitmonchan. Lets say you have a Fossil Magmar up against TR Hitmonchan
  and you want to smog it and TR Chan did Cross Counter last turn. You
  have 30 damage and Chan has 40. You can attach Charity to Magmar then use smog
  to posion it and reduce the damage to zero. If you poision him you wont have
  to worry about being hurt becuase Cross Counter only does damage dealt from
  attacks, not effects of attacks.So in result Chan will die...er...faint at the
  end of their turn if not retreated you no damage will be done to you by Cross
  Counter. This card I think will be used against TR Hitmonchan more than
  Mr. Mime I think. It will be useful against him still but I think it will be
  more effective against Chan. It is best combo'd with Pokemon with Status
  effects so I wouldn't use it if you Pokemon didn't have any status effect
  attacks like poision,sleep,smokescreen,etc.It's not for every deck, but if you
  you have the right Poke's, it will be great.
   
  Thanks for reading everyone. Hope you find this
  advice useful.
   
  The Mature Gohan