Can a Hidden Tideturner swap locations with a unit from another battlefield, given that hidden units must normally choose targets at their location?

Ruling: Yes, Tideturner works as intended despite the general hidden targeting restriction. Because Tideturner's ability explicitly requires targeting "a unit you control at another location," which makes the normal hidden targeting restriction impossible to fulfill, it is allowed to choose targets freely from among available options.

Nuances:

• This requires errata on Tideturner to function correctly
• The general rule is that hidden cards must choose targets from the battlefield associated with their facedown zone
• An exception exists when an ability has a targeting restriction that can never be fulfilled by units at its battlefield