Do I have to mark the Energy from Butcher of the Sands differently because it is restricted?

The Core Rules state Energy has no physical marker by default and players may use a physical tracker if retaining unspent Energy [165.3], but they do not provide a required method for tagging restricted Energy. Because the ability places a restriction on how its Energy may be spent, you should use an agreed-upon tracking convention in your pod/tournament (for example, a distinct token or a note) or follow an official organizer ruling; the Core Rules excerpt does not mandate a single procedure [165.3].

Vendetta · VEN-141

Card text

[Reaction][>] Any domain power , Exhaust : [Add] 2. Spend this Energy only to play units or activated abilities of units.

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Butcher of the Sands

Legend · Rare

Fury

Body

is a Legend with a Reaction activated ability: pay the two rainbow-rune cost and exhaust to Add 2 Energy to your Rune Pool, with the added Energy restricted to being spent only to play units or to pay activated abilities of units. The most common misplay is assuming the Energy it adds is unrestricted (or that it can be spent on non-unit spells/abilities) — the card text limits how that Energy may be spent and that limitation matters even though the Core Rules do not fully specify how to track such a restriction.

01's ability is an activated Legend ability with the Reaction tag, so it can be activated during Closed States on either player's turn and gains the permissions of Action while it is activated .
02To use the ability you must pay its costs (the two rainbow runes printed on the ability and exhaust ). Paying costs is done in the Pay Costs step when applicable; Add Reactions may be used to add resources to pay costs during that step .
03When the ability resolves it Performs an Add: it Adds 2 Energy to the activating player's Rune Pool. Abilities that include the action Add are adding to the Rune Pool and Add effects finalize immediately when they resolve .
04Activated Add abilities with Reaction can be activated specifically while other spells/abilities are being played or resolved whenever resources are required to be paid; when activated this way the Add immediately finalizes and resolves even mid-resolution or during the Pay Costs step .
05The energy added by the ability is placed into that player's Rune Pool . The printed restriction on the ability — "Spend this Energy only to play units or activated abilities of units" — is part of the card's game text and limits legal uses of the energy the ability adds. The Core Rules show that Energy is added to a shared Rune Pool but do not provide a rule for how to tag or otherwise track Energy that has source-specific spending restrictions; that is not specified in the provided Core Rules context and so requires a judge/organizer policy or an official ruling to make practical tracking consistent in tournament play .
06Because Add is a Limited Action, players may only Add resources when Game Effects direct them to do so; Add Reactions like this one are an explicit exception that permit adding during cost payment or resolution times as described above .
07Add finalization behavior: Add resolves immediately and will resolve before other outstanding items on the chain (it does not pass priority or focus when finalizing) .

You begin to play a unit that costs 2 Energy and you don't have enough Energy in your Rune Pool; during the Pay Costs step you activate 's Reaction to Add 2 Energy.

This is allowed. During the Pay Costs step a controller may activate activated abilities with the Reaction tag that Add Energy to pay costs . Activating the ability will immediately finalize and Add the 2 Energy to your Rune Pool so they can be spent to pay the unit's cost .

You activate to Add 2 Energy, then try to spend that Energy to play a non-unit spell (e.g., a spell that is not a unit).

The card's text restricts that Energy to be spent only to play units or activated abilities of units. That restriction is part of the game text and therefore prevents spending that particular Energy on a non-unit spell. However, the provided Core Rules explain how Energy is added to the Rune Pool but do not specify a method to tag or segregate Energy with source-specific spend restrictions, so there is no procedural rule here in the provided context for exactly how to track the restriction practically — this lack of specification means a judge or tournament organizer should follow an official tracking convention or ruling for enforcing such restrictions in play .

An opponent plays a spell that creates an opportunity to pay costs during resolution (for instance, a triggered or activated effect). Can you activate to Add Energy while that other spell is resolving in order to pay that other spell's costs?

Yes, insofar as the ability is an Add Reaction. Activated Add abilities with Reaction can be activated during the playing or resolution of other spells and abilities any time those spells or abilities require resources be paid; when activated this way the Add immediately finalizes and resolves . Keep in mind the Energy added still carries the printed spending restriction on 's ability.

You attempt to activate but it is already exhausted. Can you pay the two rainbow-rune cost and Add the Energy anyway?

No. Exhausting is part of the ability's cost; you cannot pay costs during the Pay Costs step that will deterministically result in illegal choices or actions later unless you have no choice. If cannot be exhausted as part of the cost (for example because it is already exhausted and the ability requires exhausting it), then you cannot legally pay that cost to put the ability on the chain .

How to track the restriction "Spend this Energy only to play units or activated abilities of units": The Core Rules supplied explain that when a card Adds Energy it is added to the controller's Rune Pool and that Add is the action of putting resources into a player's Rune Pool , but they do not provide a formal method for segregating or tagging Energy that carries source-imposed restrictions. The Core Rules context given is therefore insufficient to specify a single authoritative tracking method for restricted Energy; judges must rely on organizer policy or an official clarification when available.
If you Add the Energy and then the unit or unit-ability you intended to spend it on becomes illegal before you spend it (for example a target becomes illegal), the provided rules do not state whether you must immediately spend or lose that Energy or how the restriction is enforced beyond the card text. The rules do say players may not pay costs that will deterministically result in illegal choices unless they have no choice , but they do not answer every permutation that can happen after Energy is Added.
Because Energy has no physical marker by default (players may use a tracker if desired) , practical enforcement of the spend-only-on-units restriction requires an external tracking convention not described in the supplied Core Rules.

Further notes

Judge note: is functionally a Reaction Add ability that also imposes a textual spending restriction on the Energy it produces. The Core Rules passages provided explain when Add Reactions can be used, that Add finalizes immediately, and that Energy goes to the Rune Pool , and they explain Reaction timing permissions . They do not, however, supply a required procedural method for tracking Energy that is restricted by source text, nor do they definitively answer every post-Add interaction (for example, what happens if the only legal uses of that Energy vanish after it is Added). Where the Core Rules are insufficient, tournament judges should follow official clarifications or organizer policy; absent such guidance, call a judge to make a ruling for that match and record a policy for later consistent application.

Can I activate during my opponent's turn to pay for a unit I want to play on my own turn later?

You can activate the ability during Closed States on any player's turn because it has Reaction and is an activated ability , but Add is a Limited Action and you may only Add when Game Effects direct you to do so. The primary, explicitly allowed timing for this ability to be used outside of Closed States is to add resources during the Pay Costs step or during resolution of other spells/abilities when resources are required . Using it purely "in advance" outside of a required payment window is not clearly allowed by the provided context.

If I activate to Add Energy while paying costs, does that Add finalize immediately or is it part of the same chain item?

Add abilities finalize immediately when they resolve, and Add Reactions activated during cost payment immediately finalize and resolve even during the resolution of other spells/abilities .

Can I spend the Energy added by to pay for activated abilities of a unit (for example, "Exhaust: deal 1 damage")?

Yes. The printed restriction on the ability explicitly allows spending that Energy to play units or to pay activated abilities of units; that is a legal use of the Energy under the card text. The Core Rules confirm that Add places Energy in the controller's Rune Pool but do not provide a mechanism for tracking the restriction beyond the card text itself .

If I Add the Energy from to pay a cost, and the spell I played is later countered, was that Energy still spent?

The provided Core Rules context does not directly address post-resolution queries about whether Energy spent remains spent if the thing played was countered. There is a relevant clarifying FAQ that confirms energy spent to play a spell is considered spent even if that spell is later countered in some cases , but the Core Rules excerpt here does not include a comprehensive rule on that interaction; consult tournament policy or an official ruling for definitive handling.

Do I have to mark the Energy from differently because it is restricted?