Bone Miser

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).

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.

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 “ 2 generic mana , Discard a card” by discarding a land card and using the black mana black mana produced to pay for the 2 generic mana .