Just a few T1 questions

[Jawman16]

Say there is an equilibrium of creatures currently in play and I control Oath of Druids.  It is now the beginning of my upkeep and I have an untapped Orchard.  How do I declare the stacking effects of Oath, if possible, to put a token into play under my opponent's control in order to Oath this turn? 

My opponent has Tolarian Academy in play.  May he/she respond to me playing my own Academy by tapping it for mana?  Since playing lands does not use the stack I am confused as to whether the opponent can respond to the land drop that will kill both of them.

Along the same lines, I play tinker and my opponent has some lands in play.  I get a Sundering Titan that kills the lands.  Can the opponent respond to the Titan effect by tapping for mana or must they respond by floating mana in response to Tinker if they are going to respond at all?

Can I get the mana from Mana Drain if I counter a instant or sorcery cast off Boseiju?

[Jacob Orlove]

1. It's not possible. You need fewer creatures before your turn begins if you want oath to trigger.

2. No. The legend rule destroys both as a state based effect before either player gets priority.

3. They can respond to the Titan's CIP effect, but you don't choose which lands die until that effect resolves.

4. Yes, it'll do everything it can, since the spell is still a legal target.

[epeeguy]

Say there is an equilibrium of creatures currently in play and I control Oath of Druids.  It is now the beginning of my upkeep and I have an untapped Orchard.  How do I declare the stacking effects of Oath, if possible, to put a token into play under my opponent's control in order to Oath this turn?

In this situation, Oath will not trigger.  Because Oath has a conditional trigger, the condition has to be true when the ability could trigger in order for it to trigger.

My opponent has Tolarian Academy in play.  May he/she respond to me playing my own Academy by tapping it for mana?  Since playing lands does not use the stack I am confused as to whether the opponent can respond to the land drop that will kill both of them.

Your opponent could not use Tolarian Academy for mana.  Both go to the graveyard before either of you can play any abilities or spells.

Along the same lines, I play tinker and my opponent has some lands in play.  I get a Sundering Titan that kills the lands.  Can the opponent respond to the Titan effect by tapping for mana or must they respond by floating mana in response to Tinker if they are going to respond at all?

Your opponent could tap his lands in response to the Sundering Titan coming into play.  Its ability does use the stack and can be responded to like any other ability (note: your opponent could always choose untapped lands when the ability resolves and you wouldn't be able to tap them for mana)

Can I get the mana from Mana Drain if I counter a instant or sorcery cast off Boseiju?

While the original instant or sorcery will not be countered, the addition of mana from Mana Drain is not dependent on this.  So, you would get mana at the beginning of your next main phase.

[Gabethebabe]

Just a note on Sundering Titan. The lands are destroyed when the ability resolves. At the moment that your opponent chooses the lands, there is no way you can respond to that.

Example.
You control a Forest and a Quirion Ranger. Your opponent plays Sundering Titan. It´s CIP ability goes on the stack. You can respond by using the Ranger´s ability and return your Forest to your hand.

When you control two Forests and a Quirion Ranger, there is not a lot you can do. Sure, you can return one of them to your hand in response to the Titan´s abililty, but your opponent will simply destroy the other one. At the moment he chooses the Forest to be destroyed, you will not receive priority to play the Ranger´s ability.

Compare this to an Avalanche Rider that comes into play, and you control two Forests and a Quirion Ranger. In thisd case you can save the Forest, because when the abilioty of the AR goes on the stack, he has to declare the target.

[Nibble]

411.2. A player may play an activated mana ability whenever he or she has priority, or whenever he or she is playing a spell or activated ability that requires a mana payment. A player may also play one whenever a rule or effect asks for a mana payment, even in the middle of playing or resolving a spell or ability.

Mana abilities don't use the stack, but you still need priority to be able to play one. There's no time between the choosing of the lands and the destruction of the lands that any player gets priority.