I don't even care how unusable Regirock is, I need that card. The artwork is amazing and Regirock is an awesome Pokemon, and horribly underrepresented in the TCG.
The Regirock would be decent in a Fairy deck as a way to protect spare energy from Hammers/Lysandre kills.
I was hoping someone would bring this card up, but a little worried that only bbninjas half gets it.
Bench a
Regirock promo (or two) on the Bench of a deck with an Energy transferring effect. Now attach
Exp. Share. For each
Regirock/
Exp. Share you save one basic Energy card every time someone of yours is KOed. Of course, most such decks are going to try to avoid losing any Energy through throwing up something big enough it can't be OHKOed and then healing it
Max Potion. Eventually
Max Potion will rotate out (likely at the next set rotation) and this can become even more valuable, though perhaps something else will be the play. Even now it offers an alternate strategy for such decks: Pokémon that normally would be too fragile to bother with (and thus don't lend themselves to the
Max Potion trick) could still work with this approach.
Still, even when its just insurance (like now) a lone Basic with a Pokémon Tool, that can't be forced Active except indirectly or via non-Trainers, and that catches a basic Energy should something be KOed seems like a good deal to me.
Edit: The most obvious use is for Fairy Transfer decks as those still see some competitive play in Standard, but there are other Energy moving effects (even more in Expanded) so I edited the post to make it a bit more general.