With the new rules for the steps of casting a spell:
A player controls Teferi, Mage of Zhalfir, and has a Leafcrown Dryad in hand. Can they cast the Dryad for its bestow cost at instant speed? Alternatively, a player controls Prophet of Kruphix, can they cast the Dryad for its bestow cost at instant speed?
There's a few related questions as to which rules apply to this scenario.

a) 108.2a states that the word “card” only refers to cards not on the battlefield or stack. If I understand this correctly, then even if we were just casting Grizzly Bears, while it's on the stack, it's not a “card”, and thus Teferi wouldn't give it flash. Does this mean that when 601.2e is checked, it discovers that it doesn't have flash, so it was cast at an illegal time? With Prophet of Kruphix, is this any different, considering that it just changes the timing rules for you?

b) Alternatively, 400.7f states that if an effect grants a card ‘an ability that allows it to be cast’, then the ability still applies to the new object on the stack. Teferi's static ability seems to grant an ability to a card in hand. What about Prophet of Kruphix, which just changes the rules on when you may cast a “creature card”.

No, you cannot. This is a change that came with Magic Origins. During 601.2b, you choose to cast it for its bestow cost instead of its normal cost. Since you're now casting it via bestow, it turn into an enchantment - aura. Then, during 601.2e, we check to see if the announcement is still legal. At that point, the bestow enchantment is not a creature, and since nothing is letting you cast an enchantment spell when you could cast an instant, the announcement is illegal and we rewind. This is also covered in the bestow rules, rule 702.102c:

702.102c The check for whether a spell can legally be cast happens after its controller has chosen whether to pay its bestow cost; see rule 601.2e.
Example: Æther Storm is an enchantment with the ability “Creature spells can’t be cast.” This effect doesn’t stop a creature card with bestow from being cast for its bestow cost because the spell is an Aura enchantment spell, not an enchantment creature spell, when the game checks whether the spell is illegal.

Nathan Long
Wizards.Com Boards NetRep