From TokenDuelist's list, I would make the following changes, using only what comes in the theme decks:
-1 Spritzee
-2 Mr. Mime
-1 Venipede
+2 Swilix
+2 Slurpuff
-2 Max Revive
+1 Tierno
+1 Great Ball
Slurpuff blocks special conditions like poison and sleep from hitting your pokemon. I must say I like the fairy abilities the XY cards bring. Xerneas accelerates your energy and has a pretty solid attack, Slurpuff blocks status moves, Aromatisse can transfer your energy at will, and fairy garden gives you free retreat. It's a rather potent set of abilities and effects.
If, later on, you're willing to add another $20 to the deck after you play it and find that you like it, you can drop the psychic pokemon to make room for 2 Jigglypuff, 2 Wigglytuff (the one with the Hocus Pinkus attack), and 2 Xerneas EX. In the trainers/energy section, you can ditch the roller skates, a couple professor's letters, and lower the total energy count to 14-15 to make room for 2 more Evosoda (great when you have 3 stage 1 evolution lines), another super potion, another fairy garden (you really want the garden in play) and some more supporters like Shauna.