Rule 811.1.d.3
If a play effect of a hidden permanent chooses any targets, those targets must be chosen from among options at the battlefield it was played to, unless the ability explicitly restricts targeting in a way that makes this impossible. Example: Blastcone Fae is a unit with Hidden and “When you play me, give a unit -2 [M] this turn, to a minimum of 1 [M].” Because this is a play effect, its target must be chosen from among units at the battlefield it was played to if Blastcone Fae was played from facedown. Example: Tideturner is a unit with Hidden and “When you play me, you may choose a unit you control at another location. Move me to its location and it to my original location.” Because its play effect has a targeting restriction that can never be fulfilled by a unit at its battlefield, its target may be chosen freely from among the available options. Example: A spell reads in part “The next unit you play this turn can be played to any battlefield.” After playing that spell, a player plays Blastcone Fae from facedown to a battlefield other than the one where it was hidden. Blastcone Fae’s play effect must choose targets from among units at the battlefield Blastcone Fae was played to, not the one it was played from.