Three cards have been added to the list of errata for the Pokémon Trading Card Game. [...] The text below reflects what the card should say, not what was originally printed. "When you attach an Energy card from your hand to Onix, remove a damage counter from Onix." This Poké-Body only works when you attach an Energy card to Onix.
Source: PUI Rules Team (2010-05-06), TPCi Errata Update (2010-05-07)

Relevant cards

Note: All applicable cards may not be listed below.
HGSS2_56