Temporal Breach

No. "Banish a unit" targets the mentioned unit,^355.10 and when you play Temporal Breach from face down, you must choose its targets from the battlefield where it was hidden.^811.1.d.2 A unit at another battlefield or a base is therefore not a legal target.

If you play Temporal Breach normally, the [Hidden] restriction does not apply. You may target an otherwise legal unit at any battlefield or base.^355.9.a811.3

No. Moving from the board to banishment makes the unit a new game object and clears its temporary modifications and statuses.^{056.1124124.1} For example, Stupefy's might reduction no longer applies, and the unit is no longer [Empowered].^124.2

The equipment detaches at the unit's previous location and does not reattach when the unit is played again. Moving the unit from the board to banishment detaches its attached cards at that last location.^719.5436.4.b The unit entering the board is a new game object, and Temporal Breach does not instruct the equipment to attach again.¹²⁴

Detached equipment at a battlefield is recalled to its controller's base during the next cleanup.^436.4.a Detached equipment at a base its controller does not control is recalled to its controller's base during cleanup.^323.6 Equipment already at its controller's base remains there.^323.6

Yes, if the unit enters the battlefield where combat is occurring and its attack or defend condition is otherwise fulfilled.^{383.4.e.2.b383.4.f.2.b} The unit entering the battlefield is a new game object, so its attack or defend condition has not been checked during that combat.^{124383.4.e.2.a383.4.f.2.a} During the cleanup after it re-enters, it gains the same attacker or defender designation as its controller.^466.2.c.3.a Gaining that designation checks the corresponding attack or defend trigger.^{383.4.e383.4.f}

No. "You" in Ravenbloom Conservatory's ability means its controller, so if you control Ravenbloom Conservatory, it checks its "When you defend here" condition when you gain the defender designation as combat opens.^{190.6.d383.4.f466.2.c.3} That defend condition is checked only once per combat.^383.4.f.2.a

The unit becomes a new game object, but Ravenbloom Conservatory does not.¹²⁴ As the defending player, you keep the defender designation until combat ends, so the unit's return does not cause you to gain it again.^468.7.a

The token ceases to exist in banishment, so its owner cannot play it again. Tokens can exist only on the board or the chain and cease to exist immediately after entering another non-board zone.^{056.1186186.1}

Yes. Playing the unit "ignoring its cost" sets only its base energy and power costs to zero.^356.1.b.1 Additional costs apply afterward and can raise the total cost above zero.^356.1.b.3 As the unit's owner, you may therefore choose and pay an optional additional cost during finalization.^{355.1.a356.2.b.1} For example, [Accelerate] remains available because it is an optional additional cost paid while playing the unit.^805.2

The attempted play is cancelled, and the unit returns to its owner's banishment. Temporal Breach sets only the unit's base energy and power costs to zero, so mandatory additional costs must still be paid.^{356.1.b.1356.2.a.1} If the owner cannot pay one, the play fails its cost check.^358.2 The play is then cancelled and its actions are undone, returning the unit from the chain to its owner's banishment without undoing Temporal Breach's earlier, completed instruction.^354358.5

No. Hide is a separate action, not a way to play a card.^811.1.c.1 Playing puts the unit on the chain for finalization, while hiding would put it facedown at a battlefield.^420.1422.1 The unit is also in banishment, but [Hidden] permits hiding only from hand or the champion zone.^811.1.b

No. You retain control of the battlefield while Temporal Breach banishes your only unit there and that unit is played again, so you do not conquer it again.^471.1 The unit remains pending on the chain through cleanup, so you do not lose and regain control of the battlefield.^{323.5330334.2} Cleanup can remove your control of an empty battlefield only when no chain exists.^190.4.c309.1

Steps

1. Banishment leaves you with no units at the battlefield and incurs a cleanup, but that cleanup waits for Temporal Breach to finish resolving.^319.6321.1

2. The unit's owner begins playing it by moving it to the chain, where it remains pending while Temporal Breach finishes resolving.^{354354.2354.3}

3. The pending unit remains on the chain throughout the cleanup, so you retain control.

4. The unit then finalizes and enters the same battlefield under its owner's control.^{191.2191.4334.2337.1359.2.c}

Both effects can stop the unit from being played and leave it in its owner's banishment, but Rockfall Path does not stop the play process from starting, while a resolved Brynhir Thundersong effect that applies to the unit's owner does.

With Rockfall Path, the owner begins playing the unit, moving it from banishment to the chain as a pending card.^{354354.2420.3.b} Its finalization waits until Temporal Breach finishes resolving.^354.3 Temporal Breach requires the unit to be played to its previous location, but Rockfall Path forbids units from being played there, so the unit fails its legality check.^{355.17355.17.b358.1} That play is cancelled and undone, returning the unit to its owner's banishment.^358.5

With Brynhir Thundersong, the owner cannot begin the play game action, so the unit never leaves banishment.^{054.1420.3.c420.5} The impossible play instruction is negated, and Temporal Breach continues resolving after doing as much as possible.^{055358.3.a359.3.e.6}