When I use Re'sai's ability, should I pay for the cost of the card I took?

Question

Accepted Answer

If Rek'Sai's ability causes you to play a card, you must follow the normal play process for that card and pay its costs unless the ability explicitly changes or removes those costs.

Yes — when you play the card taken with Rek'Sai's ability, you must determine and pay its costs as you would for any play, unless the ability text explicitly says the card is played for a specific cost or ignoring its costs. You may use Add Reaction abilities to add resources while paying costs. See the rules cited below for exact timing and exceptions.

If Rek'Sai's ability causes you to play a card, you must follow the normal play process for that card and pay its costs unless the ability explicitly changes or removes those costs.

Final Ruling

Yes — when you play the card taken with Rek'Sai's ability, you must determine and pay its costs as you would for any play, unless the ability text explicitly says the card is played for a specific cost or ignoring its costs. You may use Add Reaction abilities to add resources while paying costs. See the rules cited below for exact timing and exceptions.

Citing

01If Rek'Sai's ability causes you to play a card, that play begins the normal play process (it becomes an item to be finalized and resolved). See rules on determining total cost .
02Determine the card's Total Cost: apply any "play for [Cost]" replacement or any "ignore costs" instruction first; then add mandatory and optional additional costs; then apply cost increases and discounts .
03Pay costs in the Pay Costs step: pay combined Energy and Power, and any non-standard costs. During this step you may activate Reaction Add abilities to add resources to pay those costs .
04

If Rek'Sai's text explicitly says "play it ignoring its cost" then you do not pay the card's printed Energy/Power costs (but optional additional costs you chose to pay may still matter per 356.1.b and 356.4.f) [356]. If Rek'Sai's ability says "play it for [Cost]", replace the card's base costs with that cost instead of paying the printed cost [356.1.a]. If a Mandatory Additional Cost (e.g., from a Passive Ability or Deflect) applies to the card, you must satisfy it to complete the play even if the card was obtained via Rek'Sai's ability [356.2.a] [809]. If paying an additional cost would "kill" Rek'Sai but another replacement effect (like Zhonya’s Hourglass in the example) replaces that death, the cost is still treated as paid [357.2.a]. You can activate Reaction Add abilities to generate Energy/Power during the Pay Costs step; Add abilities finalize immediately and resolve before further finalization [429.3] [429.2].

When an ability (for example, an ability on Rek'Sai) causes you to play a card, you follow the standard "play" procedure for that card. That means you must determine the card's Total Cost and pay those costs unless the ability text explicitly replaces or removes those costs [356]. The Determine Total Cost step explains that if an instruction allows you to "play a card for [Cost]" you replace the card's base costs with that cost, and if an instruction allows you to "ignore" one or more costs you set those components to zero; otherwise apply mandatory and optional additional costs, cost increases, and discounts in the order described [356].

You pay the card's costs in the Pay Costs step: pay combined Energy and Power and any non-standard costs. During that step you may use activated Reaction abilities that Add resources to add Energy and Power to pay those costs; Add abilities finalize and resolve immediately when used in this way [357] [429.3]. If an additional cost is an event that gets replaced by another effect (for example, a unit you killed as an additional cost is instead destroyed by a replacement effect), that cost is still considered paid [357.2.a].

Costs that appear as "costs within instructions" on triggered abilities are paid on finalization of that triggered ability, per the definition of costs within instructions [742.1.b]. If Rek'Sai's ability itself is a triggered ability that contains a cost within instructions, that cost must be paid on finalization of the triggered ability in order to place the triggered ability on the chain [742.1.b].

Finally, practical examples in the official clarifications show similar interactions: the FAQ confirms that if you play a card via a special route but still pay a specific cost (e.g., pay Accelerate), other resulting effects still apply (e.g., the Accelerate delayed replacement effect causes the unit to enter ready) even if paying an additional cost involved the controller's own permanent (like killing Rek'Sai) [FAQ:unleashed#24].

Therefore: unless Rek'Sai's ability explicitly says the card is played for no cost or for a specified alternative cost, you should determine and pay the normal costs (and any additional mandatory costs) for the card you take, using Add Reactions as needed to generate resources during the Pay Costs step.