po·ly·pho·nic (adj.):
composed of relatively independent melodic lines or parts; many-voiced.
Probably the most basic deck you could make with these sum total parts. The stars here are obviously Poliwrath with the trusty Politoed on deck behind it, and it's only unfortunate that you can only have one of each on deck (since you can only carry two Poliwags). On its own, Poliwrath is nothing to write home about; with its partner on the bench, it can be a force to be reckoned with—Politoed's Lordly Cheering will amp up Mega Punch to a respectable 120 damage for only 3 Energy (with any luck, a single Misty can get you there by Turn 3). Its Counterattack ability stacked up with a Rocky Helmet will do 40 damage to any opponent that attacks into it haphazardly, for a total 160 damage.
For backline support, you have (CG) Primarina, effectively becoming a once-per-turn Irida to keep your Pokémon topped up, and a single Lillie is there for supplemental healing of any of your Stage 2s. (Plus 60 damage for 2 Energy is nothing to scoff at, so in the case you absolutely need to play it at the start of a match, it doesn't completely break your energy curve.) And of course, if your opponent is pestering you with TRG or Banette, that's why we have Vaporeon—the ability to move Energy freely can be a massive boon, and it's another 120 HP body in case you need a bit of added protection.
As for Supporter cards, it's fairly standard. Only one Leaf since none of your Pokémon have a retreat cost above 2 (Lyra would just be overkill), and it will only be crucial for trouble in the early game, or an emergency switch if an opponent Sabrina's you. Tweak the Trainers to your liking.
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Below is a more offensively oriented version of this deck with the same general premise, except geared around using Greninja to poke the bench and Cyrus to draw unprepared foes to the active area before Poliwrath slams into them. Leftovers can be given to Poliwrath for some level of sustainability, or exchanged for whatever Tool you prefer—Giant Cape to stop Greninja getting OHKO'd by most threats; Rocky Helmet to make enemies apprehensive to attack you; even Poison Barb could work to get a tiny bit of chip on someone.