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
Now the card has almost quintupled in value over a month due to its synergy with Ashling, the Limitless, the face commander of the Dance of the Elements Commander precon
That's because you get to choose a number between zero and 13, before each player has to sacrifice that many creatures
Some people will have better luck and some will have worse luck
While some cards like Hidden Courtyard require activation to discover X, the new mechanic itself is defined as a keyword action that resolves if the ability on the stack does
It'll work for Auras, normal enchantments too, Classes, and even if countered will still draw you that card