My idea, which I am hoping to test soon, and which I believe has more potential than either Zygarde or Lucario (partly because of the prize exchange) is a Primal Clash Medicham/Safeguard Carbink/Break/Regirock; my own idea was that, to maximise damage output, include 4 Regirock-EX. Get three out with Ultra Ball/Hoopa, while making bench space with Sky Field instead of fighting stadium. I wasn't sure about the change at first, but it didn't take long for me to realise that sky field allowed for more space, more Regirock, and more than just and a maximum of 40 instead of merely 20 damage...which, in the case of Medicham, is more like 80 over 40. A big difference. Plus, a lot easier to get multiples of into play for fast, furious damage. If Sky Field gets taken down and you are forced to discard, use Buddy-Buddy Rescue or Super Rod. And don't forget, you already have Carbink with safeguard (and an awesome Break attack) plus Muscle Band and Strong Energy; in Unlimited, you could use Pluspower instead, but that isn't really an option at present.
As for getting a Lysandre'd Regirock out of play? It's really the same as with Hoopa and Shaymin, except that you want to keep it in play after playing it. Personally, I might use Hex Maniac, as it, along with 4 VS Seekers and other Supporter techs, works well in this deck, since you will be aiming to discard Strong Energy using Battle Compressor from turn one. And after that, it's just Switch (best card in the game), or AZ, or Scoop Up. Alternatively, one could use Marowak as a 1-1 or 2-2 line for help against item lock. If it's that you think Regirock is easily able to get pulled into the active spot and KO'd (and that's the reason you don't want to play it) then I would think about reconsidering the Shaymin, as well. Just saying, it has way more HP, even though the attack isn't that great and the retreat is high. Another option to counter this is a 2-2 Zoroark line.
If you are only playing a Lucario or Zygarde deck, you will probably only need one or two, simply because they don't share the Omega Barrage trait and, therefore, cannot utilise the full potential or Regirock's boost; 10 or 20 extra damage is only a little boost, but when messing with Medicham keep in mind that those numbers are doubled.
(Sorry about the long post, but nobody ever seems to even think of Medicham as an option. Guess I just love the art too much).