Item: Flame Orb
EVs: 252 HP/128 Defensive/128 Spd
This set is obvious. With Shendinja's terrible HP stat, Ev training in defenses is necessary. Substitute allows him to survive a few hits. Sandstorm can allow damage to the opponent while Shedinja takes it. Endure allows him to take a turn, to allow Flame Orb to turn on. Harden allows a raise in Shedinja's defensive. This set really is undefeatable!
You have been blessed with the gratitude of reading the Other Gyarados's post. May you have luck in the future.