If Magearna EX with the "Mystic Heart" Ability is in play, are all Pokemon with Metal Energy attached protected from Greninja's "Shadow Stitching" attack?
If Magearna EX has a Metal Energy attached to it, all Pokemon with Metal Energy attached are protected; however, if Magearna EX does not have a Metal Energy attached to it, its Mystic Heart Ability is shut off and no Pokemon with Metal Energy attached are protected.
Source: TPCi Rules Team (2017-02-02)

Relevant cards

Note: All applicable cards may not be listed below.
XY11_110
XY11_75
XY9_40