While it is trivial to get twenty or more creatures on the battlefield, if you have that many creatures, you can probably just win with those creatures
Twilight Sparkle is thematic for a "group hug" deck, which means that you're going to give your opponents a lot of opportunities to draw cards and yourself a lot of opportunities to get Treasure
Its a creature deck at heart and can easily run over tables with a wide board full of 5/5 creatures with flying, haste, first strike, vigilance, unblockable, and whatever other keywords you can jam in
Those cards can appear in randomised booster packs or in dedicated box sets depending on the release
Mischievous Quanar: One of my favorite cards ever, I keep forgetting that the awesome part of copying the spell is cheaper than turning it face down again