Enchanted creature has haste and "At the beginning of your upkeep, destroy this creature. Reveal cards from the top of your library until you reveal a creature card. Put that card onto the battlefield and attach Shifting Shadow to it, then put all other cards revealed this way on the bottom of your library in a random order."
If you don't reveal a creature card this way, you'll just reveal and randomize your library and Shifting Shadow becomes attached to nothing. It will be put into its owner's graveyard as a state-based action.
2017-08-25
wotc
If the Shifting Shadow leaves the battlefield after the triggered ability it grants has triggered but before it resolves, you'll destroy the creature it enchanted before it left the battlefield, then reveal cards and put a creature card onto the battlefield. Shifting Shadow won't become attached to it. The same is true if the enchanted creature leaves the battlefield rather than just Shifting Shadow, except that you won't destroy the creature it enchanted in that case.
2017-08-25
wotc
If the enchanted creature can't be destroyed, most likely because that creature has indestructible, you'll still get a new creature and attach Shifting Shadow to the new creature.
2017-08-25
wotc
If Shifting Shadow can't become attached to the creature you put onto the battlefield, most likely because that creature has protection from red, it becomes attached to nothing. It will be put into its owner's graveyard as a state-based action.
Format Legality
Standard
Not Legal
Future
Not Legal
Historic
Not Legal
Timeless
Not Legal
Gladiator
Not Legal
Pioneer
Not Legal
Modern
Not Legal
Legacy
Legal
Pauper
Not Legal
Vintage
Legal
Penny
Not Legal
Commander
Legal
Oathbreaker
Legal
Standardbrawl
Not Legal
Brawl
Not Legal
Alchemy
Not Legal
Paupercommander
Not Legal
Duel
Legal
Oldschool
Not Legal
Premodern
Not Legal
Predh
Not Legal
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