Ok so the first scenario where a single spell is cast with the two out. Step 5 is where my question comes into play and it isn't described on the website
1. The player cast the spell. It is now on the stack.
2. Knowledge Pool's ability triggers and is now placed on the stack above the spell.
3. Priority is passed twice and resolution begins.
4. Knowledge Pool's ability resolves and the original spell is exiled.
5. You may now cast any spell that has been exiled by Knowledge Pool, excluding the spell you cast that triggered this ability.
a. Knowledge pool creates a new stack directing a player to choose a spell from knowledge pool
I see 1 of 2 possibilities here, both bypass Teferi. If there is a third+ please let me know. The first is probably the most likely as I've not
seen a precedent for the 2nd.
1. The new stack resolves prompting the player to choose a spell from the pool which is added to a new (empty) stack allowing the player to cast
the spell as normal on their turn.
2. The new stack resolves, replacing Knowledge Pool's triggered ability with the new spell on the stack and otherwise an empty stack allowing
sorcery speed casting
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You don't "create a new stack" upon casting a spell. Rather, in general there is only one stack (C.R. 400.1), and as part of casting a spell, you put that spell on the stack on top of anything already there (C.R. 405.2, 601.2).
However, if an opponent of yours controls Teferi, Mage of Zhalfir or Teferi, Time Raveler, you can't cast any spell while Knowledge Pool's second ability is resolving, even if it's your main phase, since that ability would still be on the stack at that time so that, because the stack isn't empty, it won't be a time that any player "could [normally] cast a sorcery" (C.R. 117.4, 608.2c, 307.5, 101.2; see also C.R. 117.1a, 601.3, 608.2g). (Note that the ability leaves the stack only after its instructions are carried out [C.R. 608.2, 608.2c, 608.2m].) See also this thread and this thread. As a result, since you can't cast any spell this way, you can't choose to do so and Knowledge Pool's second ability does nothing further but exile the spell that made the ability trigger (C.R. 608.2d, 609.3).
Also, note the following:
The stack itself doesn't resolve, but rather individual spells and abilities in it do, with priority windows in between (C.R. 117.4, 117.3b).
The comprehensive rules never speak of "speed" with respect to sorcery or instant spells.
But on step 5 it's ability has to resolve for you to pick a spell, or for the spell to cast. If that's not the case then you can NEVER counter an activated or triggered ability because it's "resolution" would already be on the stack. It seems as if people stop considering the "stack" order at step 4 in the order I copied above and simply say everything below that happens simultaneously, which it does not. See below. with only 1 stack it has to be one of these two
Activated ability goes on stack
responses > This is where you could cancel the activated/triggered ability
activated ability resolves to "cast" spell
stack is empty after ability resolves and spell is cast
If it works the way people are saying it does
Activated ability goes on stack
Spell goes on stack on top of it
Counter activated ability goes on stack
stack resolves and activated ability is canceled but spell resolves because it is already on stack and because resolving a cast spell only checks for valid targets
Indeed, Knowledge Pool's second ability has to resolve for a player to cast a spell with it, but it also has to resolve for that ability to exile the spell that made it trigger (C.R. 603.2). (To be clear, both of Knowledge Pool's abilities are triggered abilities, not activated abilities [C.R. 603.1; compare with C.R. 602.1].)
Take the following scenario:
Assume it's your main phase, you have priority, you control Knowledge Pool, and an opponent of yours controls Teferi, Mage of Zhalfir or Teferi, Time Raveler.
You cast Divination, putting it on the stack among other things (C.R. 608.2, 117.1a). Knowledge Pool's second ability triggers (C.R. 608.2i, 603.2). (Although the ability triggers, it does nothing yet at this point [C.R. 603.2].) Then you put that ability on the stack (C.R. 603.3).
At this point, both Divination and the Knowledge Pool ability are on the stack, the former below the latter. Before either resolves, players will eventually get priority to cast spells targeting the former (such as Cancel) or spells targeting the latter (such as Stifle) (C.R. 117.3d, 117.1a). Assume, however, that instead all players pass.
Now, the Knowledge Pool ability resolves. Divination is exiled, but because Knowledge Pool is still on the stack, it won't be a time that a player "could [normally] cast a sorcery", so you can't choose to cast any spell from among cards exiled with Knowledge Pool. Thus, all that remains for the Knowledge Pool ability is to leave the stack.
Now consider an alternative scenario.
Step 1 is the same.
Step 2 is the same.
Now assume that you and other players pass until Teferi's controller gets priority, then Teferi's controller casts Stifle targeting the Knowledge Pool ability.
All players pass, then Stifle resolves and the Knowledge Pool ability is countered.
All players pass, then Divination resolves. You draw two cards, then Divination goes to the graveyard.
Now consider a third scenario.
Step 1 is the same.
Step 2 is the same.
Now assume that only you and other players pass until Teferi's controller gets priority, then Teferi's controller casts Cancel targeting Divination.
All players pass, then Cancel resolves and Divination is countered.
All players pass, then the Knowledge Pool ability resolves. Since Divination is no longer on the stack, it isn't exiled and the ability does nothing further (C.R. 118.12).
Ok so the first scenario where a single spell is cast with the two out. Step 5 is where my question comes into play and it isn't described on the website
1. The player cast the spell. It is now on the stack.
2. Knowledge Pool's ability triggers and is now placed on the stack above the spell.
3. Priority is passed twice and resolution begins.
4. Knowledge Pool's ability resolves and the original spell is exiled.
5. You may now cast any spell that has been exiled by Knowledge Pool, excluding the spell you cast that triggered this ability.
a. Knowledge pool creates a new stack directing a player to choose a spell from knowledge pool
I see 1 of 2 possibilities here, both bypass Teferi. If there is a third+ please let me know. The first is probably the most likely as I've not
seen a precedent for the 2nd.
1. The new stack resolves prompting the player to choose a spell from the pool which is added to a new (empty) stack allowing the player to cast
the spell as normal on their turn.
2. The new stack resolves, replacing Knowledge Pool's triggered ability with the new spell on the stack and otherwise an empty stack allowing
sorcery speed casting
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-MadMage
However, if an opponent of yours controls Teferi, Mage of Zhalfir or Teferi, Time Raveler, you can't cast any spell while Knowledge Pool's second ability is resolving, even if it's your main phase, since that ability would still be on the stack at that time so that, because the stack isn't empty, it won't be a time that any player "could [normally] cast a sorcery" (C.R. 117.4, 608.2c, 307.5, 101.2; see also C.R. 117.1a, 601.3, 608.2g). (Note that the ability leaves the stack only after its instructions are carried out [C.R. 608.2, 608.2c, 608.2m].) See also this thread and this thread. As a result, since you can't cast any spell this way, you can't choose to do so and Knowledge Pool's second ability does nothing further but exile the spell that made the ability trigger (C.R. 608.2d, 609.3).
Also, note the following:
Activated ability goes on stack
responses > This is where you could cancel the activated/triggered ability
activated ability resolves to "cast" spell
stack is empty after ability resolves and spell is cast
If it works the way people are saying it does
Activated ability goes on stack
Spell goes on stack on top of it
Counter activated ability goes on stack
stack resolves and activated ability is canceled but spell resolves because it is already on stack and because resolving a cast spell only checks for valid targets
Take the following scenario:
Now consider an alternative scenario.
Now consider a third scenario.