Baron Nashor

No. Baron Nashor enters the Baron Pit directly; he does not move there.

Moving means changing position between spaces on the board, while entering the board from another zone is a zone change.^448.1448.2 When Baron Nashor creates the Baron Pit, his replacement effect changes his entry location from the originally chosen location to the Baron Pit.^369.3

Yes, if you choose Hunters' Circle as Baron Nashor's play location and he is the first unit or gear you play there on your turn; Hunters' Circle reduces his cost by 1 even though he enters the Baron Pit instead.

A unit's play location is chosen before its cost is determined, so Hunters' Circle's discount applies.^355.2356.4 Baron Nashor's replacement effect later changes only where he enters.^369.3 It does not change his chosen play location.^355.15 His cost has already been determined and paid by then, so it is not recalculated.^{356357359.2.c}

If you control The Exile and choose a battlefield you control as Baron Nashor's play location, Baron Nashor enters the newly created Baron Pit ready regardless of which replacement effect applies first.

The Exile checks the battlefield Baron Nashor was played to, not the battlefield where he enters. The chosen battlefield remains his play location when his replacement effect changes his entry location to the Baron Pit.^{355.2355.15369.3} One replacement effect changes the entry location, and the other makes Baron Nashor enter ready. Applying either one first leaves the other applicable to Baron Nashor's modified entry.^370.1370.2 The effects can be applied in either order.³⁷² Both orders therefore produce the same result.

Baron Nashor's entry contests the newly created Baron Pit and leads to a non-combat showdown there. The Baron Pit remains uncontrolled until that showdown closes.

Entry and Showdown Opening

1. The Baron Pit is created uncontrolled.^440.4.b

2. Baron Nashor enters it and contests it for his controller.^190.3.a.1

3. His entry causes a cleanup, which stages a showdown at the Baron Pit.^319.6316.8.b

4. That showdown normally begins during the cleanup. If multiple showdowns are ready to begin, the turn player chooses which one begins.^323.11

5. The Baron Pit remains uncontrolled while the showdown is ongoing.^190.4.b

Closing and Conquest

The showdown closes after every player passes focus in sequence without playing a card or activating an ability.^347.2.a348 If Baron Nashor's controller is then the only player with units there, they establish control of the Baron Pit and conquer it if they have not scored it that turn.^{348.2.a348.2.a.1}

Yes, when the potential winning point would come from conquering. At match point, a player gains the final point from a conquer only if they have scored every battlefield on the board that turn, including the Baron Pit.^{473.1.b473.1.b.1} If they have not scored every battlefield, they draw a card instead.^473.1.b.1

Yes, if the unit does not have lethal damage when the cleanup checks it while Baron Nashor's +2 still applies. The cleanup checks all units for lethal damage only once, so a unit that becomes lethal after Baron Nashor leaves is not checked again during that cleanup.^323.4

Steps

Suppose Baron Nashor is assigned lethal combat damage and a friendly Evelynn, Entrancing is assigned 2 combat damage.

1. Lethal-damage check: Baron Nashor has lethal damage, while Evelynn's 2 marked damage is less than her current 4: her printed 2 plus Baron Nashor's +2.^142.4.b Of the two, only Baron Nashor has lethal damage during the check, so the cleanup kills him and not Evelynn.^323.4

2. Baron Nashor's passive ability stops applying when he leaves the board.^365.1 Evelynn therefore returns to 2 after the lethal-damage check has finished. Her 2 marked damage is now lethal.^142.4.b That cleanup does not check her again.

3. Combat healing: The combat special cleanup heals all units, clearing Evelynn's marked damage.^468.1.a.1

4. Baron Nashor's departure causes another cleanup.^319.6322 Evelynn has no marked damage when that cleanup checks for lethal damage, so she is not killed.^323.4

Yes. You choose your base as Baron Nashor's play location because Mageseeker Warden makes it the only legal option.^355.2355.2.a

If the Baron Pit is not on the board, Baron Nashor's "as you play me" instruction adds it and his replacement effect changes his entry from your chosen base to the Baron Pit.^{135.2.b.3369.3}

If the Baron Pit is already on the board, Baron Nashor does not add it, so the conditional replacement does not apply and he enters your chosen base.^359.2.c369.3