Can you use Ambush to play a unit into your base at reaction timing?

Ruling: No. The [Reaction] timing granted by Ambush only applies when playing the unit to a battlefield where you control units. When playing a unit to your base, the Ambush condition is not met, so the unit must be played at [Action] timing during an open state.

Nuances:

• You can always play an Ambush unit to your base, but only at normal [Action] timing.
• Ambush adds an additional valid location (battlefield where you control units) and grants [Reaction] timing only for that specific play location.
• The [Reaction] timing benefit is conditional and does not apply to plays that don't meet the keyword's requirements.