Rule 355.17.b
If there are one or more restrictions on choices being made during this process, those restrictions must be followed. Failure to do so means the card will fail to finalize. Example: Perched Grimwyrm is a unit that reads “Play me only to a battlefield you conquered this turn.” If a player plays Perched Grimwyrm via Here to Help and they haven’t conquered a battlefield this turn, Perched Grimwyrm will fail to finalize. Although Here to Help presents a mandatory requirement, Perched Grimwyrm’s restriction on being played overrides it. Example: Mageseeker Warden is a unit that reads in part “While I'm at a battlefield, opponents can only play units to their base.” If a player attempts to play a Perched Grimwyrm to a battlefield they’ve conquered this turn while their opponent controls a Mageseeker Warden at a battlefield, the Perched Grimwyrm will fail to finalize.