AI DraftFeb 26, 2026
Aetherflux Reservoir + Karn, the Great Creator
Overview
If Karn, the Great Creator is controlled by an opponent of the Aetherflux Reservoir’s controller, Karn’s static ability prevents that opponent from activating Aetherflux Reservoir’s “Pay 50 life: This artifact deals 50 damage to any target.” ability — a player can’t begin to activate an ability that’s prohibited from being activated ; activation is a defined process that creates an activated ability on the stack and requires paying activation costs (paying life is a cost) . If Karn is controlled by the same player who controls the Reservoir, Karn’s static ability does not stop that player from activating the Reservoir.
Step 1
Scenario: Opponent controls Karn and you control Aetherflux Reservoir. You attempt to use the Reservoir's activated ability. You may not begin to activate that ability while Karn's static ability applies — a player can't begin to activate an ability that's prohibited from being activated .
Step 2
Because you can't begin activation, you never announce the activation and you never create the activated ability on the stack under the process described in . The activation is illegal to start, so nothing is paid and nothing is put on the stack.
Step 3
If instead Karn is controlled by the same player as the Reservoir, Karn's static ability doesn't apply to that Reservoir. The Reservoir's controller announces activation and follows the activation process: announce activation and create the ability on the stack , then pay the activation cost (paying 50 life is a cost and is paid by subtracting life per ) and complete the activation .
Step 4
If the Reservoir's activation was completed and the activated ability is on the stack before Karn's prohibition begins to apply (for example, Karn wasn't on the battlefield or its static ability didn't apply when activation began), that ability remains on the stack and will resolve normally — beginning to activate is what Karn prevents, not resolving abilities already created on the stack .
Step 5
If Karn's +1 turns the Reservoir into an artifact creature, it remains an artifact and is still affected by Karn's static ability when Karn is controlled by an opponent; being a creature in addition to an artifact doesn't remove the artifact characteristic that Karn's static ability references (and note the caveat in Ruling [2019-05-03] about when newly created creature status allows using 
abilities).
abilities).Resolution
If Karn, the Great Creator is controlled by an opponent of the Reservoir’s controller, the Reservoir’s activated ability can’t be activated while Karn’s static ability is in effect — you may not begin to activate it . If the Reservoir’s controller also controls Karn, Karn’s static ability doesn’t apply to that Reservoir and its activated ability can be activated normally (announce activation and follow the activation process in ; paying life is a cost per ). Turning the Reservoir into an artifact creature with Karn’s +1 does not remove it from being an artifact, so it remains subject to Karn’s prohibition when Karn is controlled by an opponent. An ability that is already on the stack (i.e., activation was completed before Karn’s prohibition began to apply) is not undone by Karn’s static ability — the prohibition only prevents beginning to activate while it applies .
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