Can Teemo, Strategist target units at any battlefield when his defend ability triggers, or is he restricted to his own battlefield?

Ruling: Teemo is restricted to targeting units at the battlefield where he is located.

Nuances:

• Hidden cards must choose targets from among options at the battlefield where they were hidden, unless the ability explicitly restricts targeting in a way that makes this impossible
• This applies to hidden spells and play effects of hidden permanents
• The original question referenced an erratum about hidden cards targeting anywhere, but this appears to be a misunderstanding of the actual rules