Rules Tip of the Day: You always have a hand, even if it is empty. So you can discard an empty hand, but you cannot discard a card if your hand is empty.

Q: If my opponent plays Stupor on me and I Twincast it, can I choose my opponent for the copy, or will I receive a double dose of Stupor?

A: You are the controller of this copy of Stupor; when it goes on the stack, you can either choose to not change the target of the copy and have it target you, or you can choose to have it target your opponent. As pointed out above, you are the controller of this copy, so if you do not change the target, then when it tries to resolve, it will be countered on resolution, as it does not have a legal target. So, at most, you will be 'hit' by only one Stupor in this situation.

Q: I know that a Detritivore is 1/1 in all zones if there is one nonbasic land in my opponent's graveyard. But what about a card like Sinew Sliver in my hand? Is it a 1/1, or a 2/2? I'm thinking it's a 1/1, because its ability isn't a characteristic-defining ability, but a static ability. Is that right? Similarly, what's the P/T of a Sinew Sliver in my hand if I have a Sinew Sliver in play?

A: You are correct that this Sinew Sliver card in your hand is a 1/1. You are also correct that this is because Sinew Sliver has a static ability that is only applied when it is in play, and this ability is not a characteristic-defining ability. (One way to recognize this is that characteristics defining abilities only apply to the card with the ability.) For your last question, the Sinew Sliver card in your hand will always be a 1/1, regardless of the number of effects that are applied to Slivers in play.

Q: I have Yawgmoth's Agenda in play, and my opponent has Yixlid Jailer. If I want to play a Shock from my graveyard, what happens? Does the spell go on the stack with no card text? Does it gain the card text back in time for me to make targeting decisions?

A: You can play this Shock just as if the Jailer were not in play. It will be a full and regular Shock, just as if you played it from your hand. Yixilid Jailer does not prevent you from playing any of these cards when Yawgmoth's Agenda is in play. Yawgmoth's Agenda creates an effect that allows you to play the cards in your graveyard. It does not give any abilities to these cards. When you play a spell card from your graveyard, it goes on the stack and is no longer affected by Yixilid Jailer's ability. Basically there is no interaction between these two effects; Yawgmoth's Agenda 'wins' in this situation.

Q: Can I remove the last counter on a Gemstone Mine and then sacrifice it to a Greater Gargadon before I am forced to sacrifice it to the fact that there are no counters on it?

A: No. Gemstone Mine's mana ability has you remove a counter from it and sacrifice it all as the mana ability resolves. When you activate the Mine's ability with one counter on it, you will add one mana, remove the last counter from the Mine, and sacrifice it. There is no time in this process for you to play any other spells or abilities.

Q: Magus Of The Vineyard says "At the beginning of each player's precombat main phase, add GG to that player's mana pool." Can a player play the Magus and then use the mana in the turn it was played?

A: Not unless they manage to play it before their precombat main phase begins. That ability will only trigger if it is in play when that step begins. It will not trigger if the Magus enters play during that step.

Q: Can I use Riftsweeper to shuffle a sideboard card into my deck, or just a removed from game card?

A: Cards in your sideboard are not in the removed from game zone. Effects that are applied to only those cards that are in the removed from game zone cannot affect cards in your sideboard. In order to affect a card in your sideboard you'd need to use an effect that can affect a card from outside the game.

Q: I'm playing multiplayer and I have three opponents. If I play Twist Allegiance and then target it with Radiate, what the heck happens?

A: In this example you'd have an original copy of Twist Allegiance on the stack targeting one of your opponents—let's call him player A—followed by Radiate. When Radiate resolves, two copies of Twist Allegiance, targeting the other players (Players B and C) will go on the stack. The topmost copy of Twist Allegiance will resolve first and cause you to exchange control of all creatures you control with Player C. Then the next copy will resolve and those creature that you just took from Player C will be exchanged with those controlled by Player B. Then the original copy of Twist Allegiance will resolve and case you to exchange control of creatures you currently control with Player A. In the end, Player C will end up with all of the creatures you controlled, Player B will have those that Player C controlled, Player A will control those that Player B initially controlled, and you will control all of Player A's creatures.

Q: With Martyr's Cause in play, my opponent declares he will sacrifice an Angel of Despair through it to prevent damage. There is no source or pending damage on the stack, nor is this in response to any 'targetable' damage. He wants to do this so he can reanimate it over and over, destroying something each time it comes back. Is this legal?

A: Yes. When the Martyr's Cause ability resolves, he must choose a source, but he can choose one that is not about to deal damage to him or is unlikely to ever deal damage, like an unanimated land in play. That ability can be played anytime your opponent has priority and can pay the cost.