If Rocky Helmet is attached to a Pokemon with an effect such as Donphan's "Exoskeleton" Poke-BODY or a Defender attached, will an attack that normally deals 20 or less damage trigger the effects of Rocky Helmet or not?
If the net effect of the attack results in zero damage done to the Defending Pokemon, Rocky Helmet does not trigger.
Source: PUI Rules Team (2011-12-15)

Relevant cards

Note: All applicable cards may not be listed below.
BW3_94
BW7_133
BW7_153