Can I activate Super Mega Death Rocket's ability to add it to my hand if I have no cards to discard?

Question

Accepted Answer

No. Super Mega Death Rocket!'s triggered ability requires discarding 1 as a cost to return it from your trash, and you must be able to actually discard a card to pay that cost. If you have no cards in hand you cannot pay that cost, so you cannot (successfully) activate it to return the spell to your hand. You may decline to place the trigger on the chain instead. [FAQ:unleashed#2] [422.3]

You cannot activate Super Mega Death Rocket!'s 'may discard 1 to return this from your trash to your hand' if you have zero cards in hand, because the discard is a cost that must be payable to finalize the triggered ability. If you have no cards, do not place the triggered ability on the chain (or if you do, you will be unable to pay its cost and so it won't resolve to return the card). [FAQ:unleashed#2] [422.3]

The 'When you conquer' trigger is checked and, if met, the ability may be chosen to be placed on the chain as a pending triggered ability. The 'you may discard 1 to return this...' portion is part of the choice/cost section that is paid during finalization, per splitting guidance. [FAQ:unleashed#2] If you choose to place the triggered ability on the chain, during finalization you must pay its cost (discard 1) in order for the effect ('return this from your trash to your hand') to become a finalized chain item and resolve. Costs must be actually payable when paid. [357] [422] If you have zero cards in hand you cannot discard 1 and therefore cannot pay the cost. Because discard here is a cost, you cannot successfully finalize the ability to return the card. The correct practical action is to decline placing the trigger on the chain. [422.3] [FAQ:unleashed#2]

If a replacement effect changes the discard (for example replaces the discard with something else), the act of paying the cost is still considered paid per [357.2.a]. If discard were written as part of the effect rather than as a cost, different rules (like discarding as many as possible) could apply [422.4], but here the wording and the triggered-ability splitting guidance make it a cost that must be payable [FAQ:unleashed#2] [422.3].

The text on Super Mega Death Rocket! reads: 'When you conquer, you may discard 1 to return this from your trash to your hand.' According to the triggered-ability splitting guidance, wording like 'you may [cost] to [effect]' that appears immediately after the trigger condition is treated as the player choosing whether to place the ability on the chain and then paying the stated cost during finalization if they do. [FAQ:unleashed#2] Because the discard here is a cost, the general rule about discard-as-cost applies: 'When Discarding is listed as a Cost, then the Action must be able to be completed for the cost to be paid.' That means you must actually have at least one card in hand to discard to pay the cost. [422.3]

Practically: when you conquer, you may choose to place the trigger on the chain or not. If you choose to place it on the chain you will be required to pay 'discard 1' during finalization in order to return Super Mega Death Rocket! from your trash to your hand. If you have zero cards in hand you cannot discard 1, so you cannot pay that cost and therefore cannot successfully resolve the trigger to return the card. If a replacement effect alters the discard as it would be paid, the cost is still considered paid per [357.2.a].

Therefore, with no cards in hand you should decline to place the triggered ability on the chain (or, if you somehow place it, recognize you cannot finalize it because the cost is not payable). [FAQ:unleashed#2] [422.3]