With cards that aren't officially out yet, you might want to put a translation with it.
Static Electricity: Choose a number of Lightning Energy from your deck, up to the number of Mareep cards in play (both yours and your opponent’s), and attach them to this Mareep. Shuffle your deck afterward.
It says the number of MAREEP cards, right? So what makes you think you'd have to seek out the number of Ampharos cards? You count the Mareeps, get the energy cards and attach them to Ampharos (Because "This Mareep" can be altered into "This Pokemon")