Bone Miser

• WWizards of the Coast2025-02-07
  Official Ruling
  This creature’s second ability isn’t a mana ability. It uses the stack and can be responded to. Notably, this means that you can’t pay a cost of “, Discard a card” by discarding a land card and using the produced to pay for the .
• WWizards of the Coast2025-02-07
  Official Ruling
  If you discard a card as a cost to cast a spell or activate an ability, this creature’s triggered ability resolves before that spell or ability but after you’ve chosen targets for it. If you discard a card while a spell or ability is resolving, the triggered ability resolves after you’ve finished resolving that spell or ability.
• WWizards of the Coast2025-02-07
  Official Ruling
  This creature’s abilities are triggered abilities, not activated abilities. They don’t allow you to discard a card whenever you want; rather, you need some other way of discarding a card (such as cycling).

Rulings via Scryfall