This question already has an answer here:
I was reading over various questions and it occurred to me that I might not be using Blessed Alliance as effectively as I could be. Am I able to cast Blessed Alliance after damage has been resolved, but still during combat, to make my opponent sac a creature that has been declared as an attacker? I believe I can, as 510.3 says active player gets priority and 510.2 is damage is dealt, and state based actions will be checked before active player gets priority.
Therefore, the specific example I'm asking about is, if my opponent attacks with two creatures, one I can kill with my blocker and one I cannot, can I block the one I can kill, and after it dies cast Blessed Alliance to make him sacrifice the other? I believe 510.3 means that it is still the combat phase, and his other creature is still "attacking" as defined by the rules of the game, but I am unsure.
Can instants be played after I decide not to block? I believe this question is also relevant, as the linked answer states that you can play instants during each of those phases, and end of combat is one. Are creatures that attacked still "attacking creatures" when I get priority at the end of combat?