Can you play ambush units from the trash to a battlefield with Heedless Resurrection?

Yes, you can play a unit with Ambush from your trash using Heedless Resurrection, provided it meets the cost requirements (Energy and Power) of the unit you killed as the spell's cost.

Why this works:

1. Ignoring Costs: Heedless Resurrection instructs you to "play a unit from your trash" while "ignoring its cost." This bypasses the typical requirement to pay a unit's energy and power costs.
2. Ambush is a Keyword: Ambush is a keyword that provides permissions regarding where and when a unit can be played from your hand. When playing a unit via the effect of a spell like Heedless Resurrection, you are following the instructions of the spell to "play a unit." The spell acts as the method of playing the card.
3. No Restriction on Source: The text of Heedless Resurrection specifies that the unit must be played "from your trash." The Ambush keyword does not restrict Heedless Resurrection from targeting a unit with that keyword; it simply grants additional ways to play the unit from your hand.

Important Considerations:

• Cost Requirements: You must ensure the unit you are resurrecting costs no more Energy and Power than the unit you killed as the additional cost for Heedless Resurrection.
• Battlefield Control: Per RiftJudge FAQ #9753 and Rule 187.4.c, while Heedless Resurrection is on the chain, you retain control of the battlefield, even if you killed your only unit there to pay the cost. This allows you to play the resurrected unit to that same battlefield.
• Ambush Timing: The [Reaction] timing granted by the Ambush keyword is specific to playing the unit from your hand. When playing the unit via the spell, you are following the timing and resolution rules for the spell itself.

This is my interpretation based on the mechanics of Heedless Resurrection and the Ambush keyword. No official FAQ exists for this specific interaction, but it follows the established rules for playing units from the trash.