When Mageseeker is at a battlefield preventing unit play there, what happens when you try to play a hidden unit or Sprite Call from that battlefield?

Ruling: When a hidden unit (like Teemo) is at a battlefield where Mageseeker prevents unit play, you cannot play that hidden unit at all - you cannot flip it. For Sprite Call played from hidden at that battlefield, you can play the spell itself, but you cannot play the sprite token, so the spell does nothing.

Nuances:

• The Tideturner ruling about targeting outside the battlefield only applies to hidden spells with play effects, not to permanents being played
• Sprite Call itself doesn't restrict location, but the hidden rules require the sprite to be played at the battlefield where it was hidden
• You cannot redirect the sprite to base as an alternative