Damage done to Pokémon Metal Energy is attached to is reduced by 10 (after applying Weakness and Resistance). If the Pokémon Metal Energy is attached to isn't , whenever it damages a Pokémon, reduce that damage by 10 (before applying Weakness and Resistance).
Metal Energy provides Energy. (Doesn't count as a basic Energy card.)
Episode 963 The Promise Between Ash and Pikachu
Episode 964 It is Time for Litten to Set Off!!