Time Warp is the best for its mana cost, Temporal Mastery makes your early game more explosive and is fine late, Walk the Aeons allows you to chain together multiple turns off one card when you need it, Temporal Trespass can be absolutely clutch when you need to both Time Walk and play another Howling Mine effect, and Part the Waterveil is your win condition
Fluttershy works really well with Princess Twilight Sparkle , since most Ponies, Alicorns, Pegasi, Horses, and Unicorns have tails, allowing you to buff your entire board if you build for Twilight Sparkle's kindred ability
81 PSA 10 GEM Mint grade cards exist, and that rarity, coupled with the characters iconic status, makes this a top ten pokemon card
This not only stops board wipes, but also protects your things from targeted spells and combat damage too
Use it as a surprise win condition alongside Stifle for some good times