Adversarul are in play Borborygmos Enraged, ajungem pe tura mea de attack si declar attacker Herald of Torment eu fiind la 5 viata.
El raspunde prin a da discard la un land sa imi faca mie direct 3 damage, eu raspund prin a casta Hero's Downfall pe Borborygmos Enraged si apoi adversarul raspunde prin a da discard la alt land pentru a-mi da mie 3 dmg.

Acum ce imi este clar cand se rezolva:
land discard => 3 dmg la mine
downfall => destroy Borborygmos Enraged

Ce imi este neclar:
ultima chestie de pe stack, se mai rezolva? adica eu mai primesc cei 3 dmg si daca da de ce?

Se rezolva, si primesti cei 3 damage. Raspunsul ti-l da paragraful 112.7a din Comprehensive Rules:

112.7a Once activated or triggered, an ability exists on the stack independently of its source.
Destruction or removal of the source after that time won’t affect the ability. Note that some
abilities cause a source to do something (for example, “Prodigal Pyromancer deals 1 damage to
target creature or player”) rather than the ability doing anything directly. In these cases, any
activated or triggered ability that references information about the source because the effect
needs to be divided checks that information when the ability is put onto the stack. Otherwise, it
will check that information when it resolves. In both instances, if the source is no longer in the
zone it’s expected to be in at that time, its last known information is used. The source can still
perform the action even though it no longer exists.