First, make sure you have a Shedinja, a Pokemon that knows Skill Swap, and a Ghost-Dark hybrid. This trick only works in double battles. Enter the Shedinja and the Skill Swap Pokemon into battle first, then immediately have the Pokemon that knows Skill Swap use it on Shedinja. Afterwards, switch Shedinja out with your Ghost-Dark hybrid and have the Pokemon who knows Skill Swap use it on your Ghost-Dark hybrid. Since no move can deal Super Effective damage to a Ghost-Dark hybrid, using this trick to swap Shedinja's Wonderguard over will make it invincible. However, even with Wonderguard, the Ghost-Dark hybrid will only be invulnerable to attacks. meaning that special conditions, recoil, etc. will still damage it.