It's basically a toolbox deck, that is you find the right pokemon for every situation. It plays similar to the Darkrai deck that retreats for free, except that your goal is to us Mr. Mime against heavy hitters, Mews against evolved Pokemon, Tentacruels to deal with walls, Chansey to act as a wall, and Clefairy/Clefable and Dodrios for revenge killing. Because once you have one Dodrio down retreating is free, you can repeatedly switch into whatever pokemon you need. You find whatever pokemon you need via Pokemon Trader, and so if you have the right tools you become nearly impervious to damage.
It often plays out like this: Poison a Pokemon with Tentacruel, energy removal at key times then switch into Mr. Mime to finish it off. Because Mr. Mime can never really die in one shot, you get to switch into the best response for your opponents next pokemon. Dodrio with some counters on it acts as a great revenge killer, and if left unchecked can wreck some decks.
The deck is really based around the pokepowers, as it features Retreat Aid for easy Retreating, Neutralizing Shield against evolved pokemon, Invisible Shield for attacks over 30 damage, Cowardice against small hitting attacks (as you can sponge 10/20 damage and then return it to your hand, play it again, and then retreat your active pokemon to send out Tentacool again), also utilizing the high health of Chansey to stall.
Bonus points for playing Tentacool, sponging damage, returning it to your hand, and then using Pokemon Trader to look for something you need.
There is a surprising amount of play to the deck, and it is a ton of fun in addition to being really good.