0005: Choices and costs

Status: Accepted

Context

The prototype records some choices as loose lines (PlayerA chooses red (color) for Utopia Sprawl #3, Triggered Ability from Sowing Mycospawn #15 targets Urza's Tower #11) and omits others entirely: the Sowing Mycospawn cast does not say it was kicked. Costs appear only as side effects (PlayerA: life 19, lands becoming tapped) with nothing linking them to what they paid for.

Decision

1. Choices are their own event lines, tied to the object they belong to, in the order the rules make them: modes, X, alternative and additional costs (such as kicker), then targets, then division. Choices made during resolution or as a permanent enters (such as a color) are recorded the same way, with a cause.
2. Text-based choices quote the source's wording. A chosen mode is recorded as quoted text as the source reports it, following the same approach as ability text (decision 0003).
3. Costs are recorded as costs. Anything done to pay a cost (life paid, a permanent tapped or sacrificed, a card discarded or exiled) is an ordinary event whose cause is by cost:#N, where #N is the spell or ability being paid for. A sacrificed creature (by cost:#N) is then distinguishable from one that died (by rule:sba).
4. Hidden choices are recorded as hidden. When the perspective player cannot see a choice, the line records that the choice was made without its value, following decision 0001.

Illustrative only; exact syntax is defined in the spec:

Sowing Mycospawn #2: hand -> stack by PlayerA
#2 choose kicker
#15 target #11

Mana payment is covered by a separate decision.

Rules basis

Checked against the Comprehensive Rules effective 2026-09-25.

• 601.2b: if the spell is modal, the player announces the mode; if it has alternative or additional costs such as kicker, the player announces the intention to pay them. These are the first choices recorded.
• 601.2c: the player announces targets next. A spell may require some targets only if an additional cost (such as kicker) or a mode was chosen. Target lines therefore come after the choices that enable them.
• 601.2d: if an effect is divided among targets, the division is announced.
• 601.2f: "Costs may include paying mana, tapping permanents, sacrificing permanents, discarding cards, and so on." Each of these is an event, attributed with by cost:#N.
• 601.2g, 601.2h: mana abilities are activated before costs are paid, then the player pays the total cost.
• 602.2b: activating an ability follows the same process as 601.2b to 601.2i.
• 603.3d: putting a triggered ability on the stack follows 601.2c to 601.2d, so triggers get target and division lines when put on the stack.
• 118.8, 118.9: additional and alternative costs are part of the cost, so choosing to pay them is a recorded choice.

Alternatives rejected

• Choices as attributes on the cast line (for example cast, kicked, X=3, targets #11). Rejected: choices made later (on triggers, during resolution, as permanents enter) would need a different form, and long cast lines become hard to read and parse.
• Inferring choices from later events (the prototype, where kicker is implied by the second trigger). Rejected: parsers must never guess.
• A separate cost section per spell. Rejected: costs are ordinary events (taps, sacrifices, life changes) and belong in the event stream with a cause.

Consequences

• The spec must define choice line types (mode, X, kicker and other optional costs, target, division, and resolution choices such as color) and the cost: cause form.
• Sources that cannot see the opponent's choices (likely MTGO for "them") produce hidden choice lines. That is expected, not an error.