You will need the following:
An Alakazam with Skill Swap and Role Play.
A Shedninja with U-turn. (It doesn't have to have U-turn, but it will help.)
A Spiritomb or Sableye. (Preferably Spiritomb.)
Go into a double battle with Alakazam and Shedninja, make sure your Alakazam is the fastest pokemon. Have Alakazam use Role Play on your own Shedninja, it will copy Shedninja's Wonder Guard. Then have Shedninja use U-turn. Get Spiritomb to come in battle to take Shedninja's place. Have Alakazam use Skill Swap on Spiritomb and it will have Wonder Guard. It's became a loop-hole!
Wonder Guard- An ability that makes the pokemon only take damage from super-effective hits.
Spiritomb- A pokemon that has high defense stats., and doesn't have any Super effective weaknesses.
Congratulations! If you have followed each step carefully and survived long enough to pull off this strategy, you should have an INVINCIBLE Spiritomb that won't take any hits! Battles will be easy if you do this right.
Warning: Spiritomb might take damage from side moves (Like Sandstorm and Future sight.) and conditions (Like Poison and Confusion.), there are 2 abilities that can destroy this strategy:
Mold Breaker: (Cranidos and Rampardos have this one.)
Scrappy: (Kangaskhan and Miltank have this one.)
Besides that stuff, Spiritomb is unstoppable this way!