Rule 444.2
When a player is instructed to Pay a resource, that player may remove that resource from their Rune Pool if it exists there. If they choose not to, the instruction is ignored. Example: When Diana, Lunari’s triggered ability resolves, if its controller has [1] Energy in their rune pool, they choose whether or not to pay that Energy as instructed. If they choose not to pay the Energy, they will not perform the additional effects of the triggered ability.
- 444.2.a If the instruction to Pay resources is part of paying costs for a card or ability, choosing not to pay those resources…
- 444.2.b If the instruction to Pay resources is part of paying any other cost, choosing not to pay those resources will prevent…
- 444.2.c Players may activate abilities that Add resources with the Reaction keyword at any time that they are instructed to…