i don’t understand the effect of Killing Wave… can you explain?
Killing Wave: “For each creature, its controller sacrifices it unless he or she pays X life.”
Killing Wave’s caster casts it for X and Black, where X can be any number of mana they could pay into it. Let’s say 5.
Beginning with the active player (the player whose turn it is), they choose if they want to pay 5 life to keep each creature on an individual basis. I would pay 5 life to keep a powerful creature, but not a 1/1 with no abilities. Once the active player is done making their choices, remember the ones they will be sacrificing because they didn’t want to pay said 5 life. Then the next player in turn succession does the same.
Finally, once all players have made their choices, all of the creatures that were not paid for are sacrificed at once. Note: You can’t pay for something you don’t have. So if you don’t have enough life for something, you can’t pay for it (or if you have a Platinum Emperion, but that’s different).
Also: If you can’t sacrifice a creature (perhaps because of Sigarda, Host of Herons), you can choose not to pay life and nothing will happen.