For one, Registeel/Regice/Lunatone are not necessary, although this is not to say that they shouldn't have a place in the deck. I'm just issuing a rebuttal to the people who claim it HAS to be in play for the deck to optimally function. If you start with Sableye and a Magikarp and Impersonate for a Roseanne's to grab two more Magikarp, then use Impersonate again next turn for Felicity's, discarding both of those (assuming you don't get immediately OHKOed by Kingdra/Machamp or something), you're already just one discarded Magikarp away from the magic 90. If you run VS Seeker and 4 Felicity's, the odds of you pulling one or the other out of the deck after your first Felicity's/Claydol are fairly high, and you can get all 3 Magikarp in the discard without even using Registeel/Regice/Lunatone. They're just nice back-up.
I prefer Regice, by the way, because of the option it has to disrupt and control what you KO. People commonly complain that it forces something they want to KO out of the active spot; why would this be an issue? The Power is optional, and as I already explained, it isn't necessary in setting up Tail Revenge. There will be numerous points in most games, particularly against SP, where the forced switch from Regi Move will be advantageous, ie. they go into sacrifice mode and have Crobat G active with a bench full of Luxray GLs and Claydol. Would you rather take that meaningless Crobat G or force them to give you a Luxray GL or their draw power? It also gets around Mr. Mime. Registeel has no function at all except for discarding, which can help you Cosmic Power for more but is ultimately underwhelming. I don't like it.
I've been running my list with Skuntank G, Crobat G/Poketurn, maxed PlusPower, and Cyclone energy. I admittedly got the idea for Cyclone from sixprizes.com, and it definitely does some amazing things in this deck, letting you get so many easy prizes. It's almost as good as Luxray GL lv. x when you have something hitting as hard as Gyarados for free, meaning you aren't wasting/compromising your energy drop to attach it like you would in most other decks. Incidentally, running 4 Call and 3 Cyclone lets you get around the odd Mr. Mime/Dusknoir, even though they aren't searchable. You should have enough draw power to get 3 of them into play.