Today we shall talk about a well-known character, Teferi, Mage of Zhalfir, and along that about the Flash ability and what it means to be able to “cast spells only any time you could cast a sorcery”.
Translated by Witas Spasovski
Teferi, Mage of Zhalfir
Teferi is a legendary creature. This is to say that one player may not control multiple Teferis with the same name on the battlefield, because if he or she does, the next time SBA are performed, the player will have to choose one Teferi, then put all others into their owners' graveyards. When you compose a decklist for a Legacy tournament, make sure you write his full name correctly, because recently we have had a glorious return of this character in the shape of Teferi, Temporal Archmage
Teferi has three abilities. They are all static. The zones in which these abilities function are different though.
702.8a. Flash is a static ability that functions in any zone from which you could play the card it's on. “Flash” means “You may play this card any time you could cast an instant.”
The first sentence of this rule means that we can use Flash while casting a spell from any zone. Note that Flash by itself doesn't grant you the ability to play the card from a zone other than the hand. You will need other effects to allow you to do that:
If Teferi is your Commander*, you may cast him from the command zone any time you have priority.
Haakon, Stromgald Scourge on the battlefield allows to cast any card with subtype Knight from your graveyard. If it is a creature card, you may cast it any time you have priority.
If you are the owner of Misthollow Griffin which was exiled face up, you may cast it from the exile zone any time you have priority.
The second sentence gives us the definition of Flash, and refers us to a different rule:
304.5. If text states that a player may do something “any time he or she could cast an instant”, it means only that the player must have priority. The player doesn't need to have an instant he or she could actually cast. Effects that would prevent that player from casting a spell or casting an instant don't affect the player's capability to perform that action (unless the action is actually casting a spell or casting an instant).
So, a card with Flash may be cast any time the player has priority:
Any of these cards may be cast when you have priority, including in your opponent's turn.
Mind that neither player receives priority when casting or resolving a spell, as well as activating or resolving an ability. Neither player has priority when attackers or blockers are declared, the active player gets priority only after performing these turn-based actions.
A player doesn't have cards in hand. If, while resolving Civilized Scholar's ability, the player draws Teferi, Mage of Zhalfir, he cannot cast it because he doesn't have priority. He will have to continue resolving the ability and discard Teferi.
When you begin declaring attackers, you cannot flash Izzet Staticaster in and send it to attack, because you get priority only after all attackers have been declared. This creature should have been cast earlier, like during the Beginning of Combat step.
If you move to declare blockers step, the opponent may not play Snapcaster Mage and block with it, because he will get priority only after you pass after blockers are declared. This creature should have been cast earlier, like during Declare Attackers step or before that.
Teferi's second ability functions only while he is on the battlefield. It says that all creature cards you own have Flash when they are not on the battlefield. “You” here means the controller of Teferi, so if the cunning opponent borrows your Teferi, creature cards he owns will have Flash.
You may find any creature card in your library with Mystical Teachings because Teferi gives them all Flash.
Any time you have priority you may cast a card for its Bestow cost and get an aura.
Since Dryad Arbor is a creature card, it will have Flash in your hand. You will be able to cast it any time you have priority, but only on your turn if you have not played a land until then, because it is a land as well.
You may cast any card with Morph face down at instant speed, because it turns face down in the zone you cast it from, becomes a creature right there, gets Flash through Teferi's effect, and then is put on the stack.
You may suspend a card from your hand at any time you have priority, because to perform this special action you need to a) have priority and b) match the condition “You are able to begin casting this spell by putting onto the stack”.
Be wary! Teferi only gives Flash ability to creature cards you own.
Teferi's third ability functions only when it is on the battlefield. Its effect tells us that your opponents may cast their spells only any time they could cast a sorcery, i.e. “at sorcery speed”. Let's take another look at the rules.
307.5. If a spell, ability, or effect states that a player can do something only “any time he or she could cast a sorcery,” it means only that the player must have priority, it must be during the main phase of his or her turn, and the stack must be empty. The player doesn't need to have a sorcery he or she could actually cast. Effects that would prevent that player from casting a spell or casting a sorcery don't affect the player's capability to perform that action (unless the action is actually casting a spell or casting a sorcery).
So your opponents can only cast spells while they have priority in their main phase when the stack is empty. This automatically means that any spells or abilities allowing to cast spells as they resolve are useless, because when a spell or ability is resolving, the stack isn't empty - at least that spell or ability is there.
A card with Madness cannot be cast because the Madness trigger is on the stack at this point.
A suspended card cannot be played because the stack isn't empty at this moment, the Suspend trigger is on it.
A miracle spell is cast at the resolution of Miracle trigger, so the stack isn't empty.
We are dealing with an activated ability here that's still on the stack when the copy of the imprinted card would be played.
When Knowledge Pool's trigger resolves, the opponent exiles his spell, but he cannot cast any card exiled with Knowledge pool, since the trigger is still on the stack.
Here's a totally useless spell! Since the spell is still on the stack when the effect is produced, the opponent cannot play any of the exiled cards.
If you control Teferi, none of the effects like Leyline of Anticipation can help your opponent to cast spells “at instant speed”. Such effects do not “accelerate” the opponent's spells, they simply state that a player may play cards (nonland ones) as though they have Flash. But Teferi's effect says that any spell may be cast by your opponent only at “sorcery speed”, i.e. only in his or her main phase when he or she has priority and the stack is empty.
Since the legend rule has changed, each player may control a Teferi of their own. This results in each player being able to cast spells only “at sorcery speed”.
Teferi can do many things, of course, but he isn't almighty:
Teferi doesn't prohibit your opponent to place copies of spells onto the non-empty stack without casting them. After casting Dragonstorm in his main phase while the stack is empty, the opponent will get copies off Storm.
Teferi doesn't prohibit the opponent to activate abilities any time he has priority (as long as those activations don't have any restrictions of their own).
Finally, it is fairly obvious that the spells an opponent has already cast will not be affected by a Teferi flashing into the battlefield. The spells will resolve safely if Teferi is the only countermeasure you are able to come up with.
* A Commander (or General) is a legendary creature having special properties and defining the colors used in decks in the Commander (i.e. EDH) format. Check out the rules for this alternative variant of Magic at the official site.