Could someone please confirm that the only card which can be attached with self charge is a darkness energy (a dark metal energy
cannot be attached in this way)
DarkMetal Energy only provides Darkness energy while in play ... ie. while attached to a Pokemon. While in the hand, deck, or discard DarkMetal does not provide Darkness energy thus making it an invalid target for Self Charge. Ditto for Rainbow Energy. Self Charge only works on real Darkness Energy.