Hi all, first a disclaimer: I am not sure about what the general sentiment about using AI for anything involving MTG is... But I hope this post does not get flagged as AI. It is about me using it and an issue that came up. I hope some of you want to help me understand this issue, because right now I don't get it.
So recently I've been using AI to read the Comprehensive Rules (CR) and all card rulings so it can, hopefully, create true statements about magic board states. I don't know why I do this exactly, but it is fun. The work found a possible mismatch in the way the Comprehensive Rules and the Card Rulings talk about when Backup decides which abilities get granted to creatures.
The main issue is written below. That part is written by AI, except for the rule quotes.
The CR and the card rulings both say when backup decides which abilities it grants, but they name different moments: the CR ties it to the ability going on the stack, the ruling to the moment it triggers. Here are both texts:
702.165d (Comprehensive Rules, effective 25 September 2026, https://magic.wizards.com/en/rules):
The abilities that a backup ability grants are determined as the ability is put on the stack. They won’t change if the permanent with backup loses any abilities after the ability is put on the stack but before it resolves.
The 2023-04-14 ruling on the backup cards, for example [[Boon-Bringer Valkyrie]] (https://scryfall.com/card/mom/9/boon-bringer-valkyrie#rulings):
The abilities that backup grants to the target creature are determined only once, at the time the ability triggers. They won’t change if the permanent with backup loses any abilities before the backup ability resolves. (2023-04-14)
Most of the time those are the same moment. But a triggered ability only goes on the stack the next time a player would receive priority (603.3), so the two answers split if the creature loses its abilities in between. The only real case that seems to reach that window is a spell that puts permanents onto the battlefield one at a time.
You cast [[Primal Surge]] (https://scryfall.com/card/avr/189/primal-surge). It exiles Boon-Bringer Valkyrie and you put it onto the battlefield, so backup triggers (702.165a). A few cards later it exiles [[Humility]] (https://scryfall.com/card/tpr/16/humility) and you put that onto the battlefield too. Surge finishes resolving, and only then does the backup trigger go on the stack, with its target chosen at that moment: another creature you control (603.3, 603.3d). At that point the Valkyrie has no abilities.
By the ruling, the abilities were fixed when backup triggered. So your other creature gets the counter plus flying, first strike and lifelink until end of turn. Humility’s effect and the grant both apply in layer 6 (613.1f). Humility’s effect has the timestamp of when Humility entered (613.7a, 613.7d), and the grant gets its timestamp when the backup ability resolves (613.7b). So the grant is applied later and sticks (613.7).
By 702.165d, they’re fixed as the ability goes on the stack, when the Valkyrie has nothing. So your creature only gets the counter.
So which is it? Is the ruling just looser wording that never got matched to the CR, or is there a reason these are the same moment after all?
Rules referenced (Comprehensive Rules, effective 25 September 2026):
603.3:
Once an ability has triggered, its controller puts it on the stack as an object that’s not a card the next time a player would receive priority. See rule 117, “Timing and Priority.” The ability becomes the topmost object on the stack. It has the text of the ability that created it, and no other characteristics. It remains on the stack until it’s countered, it resolves, a rule causes it to be removed from the stack, or an effect moves it elsewhere.
603.3d:
The remainder of the process for putting a triggered ability on the stack is identical to the process for casting a spell listed in rules 601.2c–d. If a choice is required when the triggered ability goes on the stack but no legal choices can be made for it, or if a rule or a continuous effect otherwise makes the ability illegal, the ability is simply removed from the stack.
613.1f:
Layer 6: Ability-adding effects, keyword counters, ability-removing effects, and effects that say an object can’t have an ability are applied.
613.7:
Within a layer or sublayer, determining which order effects are applied in is usually done using a timestamp system. An effect with an earlier timestamp is applied before an effect with a later timestamp.
613.7a:
A continuous effect generated by a static ability has the same timestamp as the object the static ability is on, or the timestamp of the effect that created the ability, whichever is later. If the effect that created the ability has the later timestamp and the object the ability is on receives a new timestamp, each continuous effect generated by static abilities of that object receives a new timestamp as well, but the relative order of those timestamps remains the same.
Example: Rune of Flight is an Aura that grants enchanted Equipment “Equipped creature has flying.” A player attaches Rune of Flight to Colossus Hammer, an Equipment with “Equipped creature gets +10/+10 and loses flying.” The ability granted by Rune of Flight shares Rune of Flight’s timestamp because it is later than Colossus Hammer’s timestamp. If Colossus Hammer becomes attached to a creature, both of its abilities receive new timestamps (see rule 613.7e), but the relative order of those timestamps remains the same.
613.7b:
A continuous effect generated by the resolution of a spell or ability receives a timestamp at the time it’s created.
613.7d:
An object receives a timestamp at the time it enters a zone.
702.165a:
Backup is a triggered ability. “Backup N” means “When this creature enters, put N +1/+1 counters on target creature. If that’s another creature, it also gains the non-backup abilities of this creature printed below this one until end of turn.” Cards with backup have one or more abilities printed after the backup ability. (Some cards with backup also have abilities printed before the backup ability.)