If you try to move Masterful Ninja from the battlefield to your hand or vice versa, and it’s in both zones, it will just stay in both zones. For example, if Masterful Ninja is in both zones, casting Unsummon targeting it won’t do anything.
Is returning Masterful Ninja to your hand an action that does nothing (compare to taking damage while controlling Platinum Emperion.
Or is returning Masterful Ninja to your hand an impossible action (compare to paying life while controlling Platinum Emperion).
I suspect it is an impossible action, but do not find the Gatherer ruling sufficiently clear on the matter, and we have no precedent I am aware of to compare to.
This question can be summed up as "Can I use Masterful Ninja to pay Ninjitsu costs?"
No situation involving Magic cards other than "silver-bordered" cards can lead to an object being in two zones at the same time; therefore, the comprehensive rules do not regulate (and therefore cannot answer) whether a cost or effect that moves Masterful Ninja from a player's hand to the battlefield or vice versa (see, for example, ninjutsu [C.R. 702.48a]) is "impossible" while Masterful Ninja is being made to appear in both zones at the same time due to its effect. (See also this thread, which involves a similar situation with the Unhinged card Yet Another Aether Vortex.)
Note that for Platinum Emperion, a special rule provides that "a cost that involves having [a] player [whose life total can't change] pay life can't be paid" (C.R. 119.9). Note also that in general, a "player can't pay a cost without having the necessary resources to pay it fully" (C.R. 118.3).
In general, in a game allowing "silver-bordered" cards such as those in Unglued, Unhinged, and Unstable, the players in the game can agree on modifications to the comprehensive rules ("house rules") to accommodate situations, such as this one, that the comprehensive rules neither regulate nor answer and that are unique to such cards (see also C.R. 100.7). Although Mark Rosewater issues "rulings" on how certain game situations unique to such cards play out, such advice is no more or less valid than the "house rules" agreed to by the players (that is, such players can agree whether to adopt such "rulings" or not).
EDIT (Jan. 2, 2019): Edited.
EDIT (Sep. 25, 2020): Some rules were renumbered in the meantime.
If you try to move Masterful Ninja from the battlefield to your hand or vice versa, and it’s in both zones, it will just stay in both zones. For example, if Masterful Ninja is in both zones, casting Unsummon targeting it won’t do anything.
Is returning Masterful Ninja to your hand an action that does nothing (compare to taking damage while controlling Platinum Emperion.
Or is returning Masterful Ninja to your hand an impossible action (compare to paying life while controlling Platinum Emperion).
I suspect it is an impossible action, but do not find the Gatherer ruling sufficiently clear on the matter, and we have no precedent I am aware of to compare to.
This question can be summed up as "Can I use Masterful Ninja to pay Ninjitsu costs?"
If a creature is already tapped, and you cast Pressure Point targeting said creature, it is still a valid spell with a valid target, so it will resolve and do as much as it can do (i.e. you will draw a card). The same applies here. You have a valid target (Masterful Ninjais a creature on the battlefield), so Unsummon is a valid spell when targeting Masterful Ninja on the battlefield. If he is also in your hand due to its ability, then Unsummon will merely do as much as it can (which is to say nothing), but it will still resolve.
True, but you cannot do an impossible action to pay a cost. Ninjustu has returning the creature as a cost, so if that is impossible, then you cannot activate that ability. That's what this thread is about. But due to the card being an Un-card and the CR being silent on those, there's no clear cut ruling.
Common sense would suggest that you can't "return" a thing to a zone that it's already in, so you cannot pay that cost.
The closest analog we have is 400.8. If an object in the exile zone is exiled, it doesn't change zones, but it becomes a new object that has just been exiled.
This suggests that a hypothetical cost of "Exile an exiled card" could in fact be paid.
Now with the Ninja, there are a few notable differences. Obviously it is not exiled, and as the Gatherer rulings do nothing to suggest it becomes a new game object (doesn't become untapped or removed from combat, affected by 'summoning sickness' if it loses Haste, or have attached objects 'fall off'), we can conclude that it remains the same object on the battlefield. Becoming a new object in the hand is a null point, being a hidden zone, even if that is the case.
The ambiguity comes from the ruling not stating that the card cannot be returned to the hand, but that doing so does nothing.
In general, where the comprehensive rules neither regulate nor answer game situations unique to Unglued, Unhinged, and Unstable cards, as in this case (see also C.R. 100.7), the players in the game can agree on modifications to the comprehensive rules ("house rules") to accommodate such situations.
Therefore, the question of "whether a cost or effect that moves Masterful Ninja from a player's hand to the battlefield or vice versa ... is 'impossible' while Masterful Ninja is being made to appear in both zones at the same time due to its effect" has no right or wrong answers.
If you use Masterful Ninja (that's both on field and in hand) to pay a Ninjutsu cost, it can't be bounced to your hand for it's already there, but it does remove it from combat.
If you try to move Masterful Ninja from the battlefield to your hand or vice versa, and it’s in both zones, it will just stay in both zones. For example, if Masterful Ninja is in both zones, casting Unsummon targeting it won’t do anything.
Is returning Masterful Ninja to your hand an action that does nothing (compare to taking damage while controlling Platinum Emperion.
Or is returning Masterful Ninja to your hand an impossible action (compare to paying life while controlling Platinum Emperion).
I suspect it is an impossible action, but do not find the Gatherer ruling sufficiently clear on the matter, and we have no precedent I am aware of to compare to.
This question can be summed up as "Can I use Masterful Ninja to pay Ninjitsu costs?"
A Dying Wish
To Rise Again
Chainer, Dementia Master
Muldrotha, the Gravetide
Atraxa, Praetors' Voice
Note that for Platinum Emperion, a special rule provides that "a cost that involves having [a] player [whose life total can't change] pay life can't be paid" (C.R. 119.9). Note also that in general, a "player can't pay a cost without having the necessary resources to pay it fully" (C.R. 118.3).
In general, in a game allowing "silver-bordered" cards such as those in Unglued, Unhinged, and Unstable, the players in the game can agree on modifications to the comprehensive rules ("house rules") to accommodate situations, such as this one, that the comprehensive rules neither regulate nor answer and that are unique to such cards (see also C.R. 100.7). Although Mark Rosewater issues "rulings" on how certain game situations unique to such cards play out, such advice is no more or less valid than the "house rules" agreed to by the players (that is, such players can agree whether to adopt such "rulings" or not).
EDIT (Jan. 2, 2019): Edited.
EDIT (Sep. 25, 2020): Some rules were renumbered in the meantime.
If a creature is already tapped, and you cast Pressure Point targeting said creature, it is still a valid spell with a valid target, so it will resolve and do as much as it can do (i.e. you will draw a card). The same applies here. You have a valid target (Masterful Ninja is a creature on the battlefield), so Unsummon is a valid spell when targeting Masterful Ninja on the battlefield. If he is also in your hand due to its ability, then Unsummon will merely do as much as it can (which is to say nothing), but it will still resolve.
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)
The closest analog we have is
400.8. If an object in the exile zone is exiled, it doesn't change zones, but it becomes a new object that has just been exiled.
This suggests that a hypothetical cost of "Exile an exiled card" could in fact be paid.
Now with the Ninja, there are a few notable differences. Obviously it is not exiled, and as the Gatherer rulings do nothing to suggest it becomes a new game object (doesn't become untapped or removed from combat, affected by 'summoning sickness' if it loses Haste, or have attached objects 'fall off'), we can conclude that it remains the same object on the battlefield. Becoming a new object in the hand is a null point, being a hidden zone, even if that is the case.
The ambiguity comes from the ruling not stating that the card cannot be returned to the hand, but that doing so does nothing.
A Dying Wish
To Rise Again
Chainer, Dementia Master
Muldrotha, the Gravetide
Atraxa, Praetors' Voice
If you use Masterful Ninja (that's both on field and in hand) to pay a Ninjutsu cost, it can't be bounced to your hand for it's already there, but it does remove it from combat.
http://markrosewater.tumblr.com/post/177553440438/greetings-mark-i-have-an-unconstructed-question
(Sorry for the month-long necro but I've been trying to get an answer on this for a while and just got it today.)