obi
formerly david stone
It could work for every Pokemon. Give Machamp BrightPowder and have it use DynamicPunch. Every time it attacks, No Guard is coming into play, and every time it's attacked, BrightPowder is bypassed (so if you are paired with EQ Garchomp).Machamp's no guard does not work for all 4 Pokemon.
http://www.smogon.com/dp/abilities/no_guard
You are correct that it won't help your ally attacking one of your opponents, though.