I ran into this bug. I had no creatures and my opponent played The Long Reach of Night. Arena prompted me to discard a card. The "Submit 0" button way grayed out. I was forced to discard a card.
I have heard from people who understand the rules of magic better than me that I should have been able to choose to sacrifice a creature, then failed to sacrifice because I had no creatures.
I ran into this bug. I had no creatures and my opponent played The Long Reach of Night. Arena prompted me to discard a card. The "Submit 0" button way grayed out. I was forced to discard a card.
I have heard from people who understand the rules of magic better than me that I should have been able to choose to sacrifice a creature, then failed to sacrifice because I had no creatures.