Can you use the Retreat spell to target a champion unit in your champion zone?

Ruling: No, you cannot use Retreat to target a champion unit in your champion zone. "A unit" refers to a unit on the board, and spells can only target units on the board unless the spell specifically says it can target units in other zones.

Nuances:

• This targeting restriction applies to all spells and abilities unless they explicitly state they can target units in other zones