There was a thread posted here that asked about the interaction between Prophet of Kruphix and cards with bestow, such as Leafcrown Dryad, and the conclusion was that casting Leafcrown Dryad using its bestow cost while Prophet of Kruphix is out is an illegal action.

I believe this is incorrect, based on the CR as currently written.

Prophet of Kruphix states that I “may cast creature cards as though they had flash.” By rule 108.2a, this means that I can cast such cards from my hand.

108.2a In the text of spells or abilities, the term “card” is used only to refer to a card that’s not on the battlefield or on the stack, such as a creature card in a player’s hand.

Because Prophet of Kruphix states that I may cast these cards “as though” they had flash, rule 609.4 takes effect.

609.4. Some effects state that a player may do something “as though” some condition were true or a creature can do something “as though” some condition were true. This applies only to the stated effect. For purposes of that effect, treat the game exactly as if the stated condition were true. For all other purposes, treat the game normally.

So, we treat the game as though the Leafcrown Dryad had flash.

But do we treat Leafcrown Dryad – as it exists on the stack as a new game object – as having flash? Yes, we do, because of rule 400.7f. Even though Leafcrown Dryad doesn't actually have flash, we pretend that it does, so 400.7f applies.

400.7. An object that moves from one zone to another becomes a new object with no memory of, or relation to, its previous existence. There are seven exceptions to this rule:

400.7f If an effect grants a nonland card an ability that allows it to be cast, that ability will continue to apply to the new object that card became after it moved to the stack as a result of being cast this way.

Having all of this, I am now allowed to cast Leafcrown Dryad from my hand.

Casting Leafcrown Dryad normally

1) Leafcrown Dryad is in my hand, with Prophet of Kruphix on the battlefield. Prophet of Kruphix gives Leafcrown Dryad the permission to be cast as though it had flash, since it is a “creature card” as the definition of “card” in rules text indicates (108.2a).

2) I cast Leafcrown Dryad. Normally, it would become a new object with no memory of its previous existence (400.7), meaning it wouldn't have any memory of the flash we treated it as having while it was in my hand. However, it keeps this permission, because we treated the game as having given it an ability that allowed it to be cast this way (400.7f and 609.4). This is okay.

3) I decide not to cast Leafcrown Dryad for its bestow cost, and instead opt to pay its mana cost as though it were any other creature spell. Note that Leafcrown Dryad remains the same object after this decision has been made.

4) I finish casting the spell, performing the relevant actions in doing so.

Casting Leafcrown Dryad for its bestow cost

Steps (1) and (2) of this process are identical to the above.

3) At this point, I decide to cast Leafcrown Dryad for its bestow cost.

702.102a Bestow represents two static abilities, one that functions while the card with bestow is on the stack and another that functions both while it’s on the stack and while it’s on the battlefield. “Bestow ” means “You may cast this card by paying rather than its mana cost.” and “If you chose to pay this spell’s bestow cost, it becomes an Aura enchantment and gains enchant creature. These effects last until one of two things happens: this spell has an illegal target as it resolves or the permanent this spell becomes, becomes unattached.”

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.

601.2e Based on the previous announcements, the game checks to see if the proposed spell can legally be cast based on applicable timing rules (including ones based on the card’s type) and other effects that may allow a spell to be cast or prohibit a spell from being cast. If the proposed spell is illegal, the game returns to the moment before the casting of that spell was proposed.

As 702.102a states, Leafcrown Dryad's characteristics change to become an Aura enchantment spell, as opposed to the Nymph Dryad enchantment creature spell that it was before. Then, 702.102c says that the check for whether Leafcrown Dryad can be legally cast for its bestow cost is performed. An object changing characteristics without changing zones does not become a new object. Thus, the flash that we treated Leafcrown Dryad as having before I decided to cast it for its bestow cost still applies, because it's “an effect that may allow a spell to be cast” as mentioned by both 601.2e and 400.7f.

This is different than what was stated in the previous thread – that because I choose to cast Leafcrown Dryad for its bestow cost that the flash we treat it as having somehow no longer applies to it, when that is not the case.

4) I finish casting the spell, performing the relevant actions in doing so.

Summary

Rule 400.7f demonstrates that the casting of a spell for its bestow cost with Prophet of Kruphix on the battlefield is legal, contrary to the answer stated in the previous thread.

Please don't lock the thread after answering – if I am wrong, please tell me how so that I can respond.

Thanks for reading.

Edited Bob Smith (Sept. 22, 2015 03:01:54 PM)