When your opponent’s Killing Wave resolves, it gives each player a choice to make for each creature that player controls: Pay X life, or don’t pay anything. If you don’t pay any life, Killing Wave says “sacrifice the creature.” If you control Sigarda, this means you can choose not to pay any life, and then you won’t have to sacrifice anything because that’s simply not possible. Of course, you could still choose to pay the life if you have strange desire to lower your life total (probably only makes sense if you’re trying to turn on Fateful Hour).
If you control Angel of Jubilation, there is no interaction with Killing Wave. Nobody is paying any life or sacrificing any creatures when casting the spell. Once the spell is resolving, anybody can pay life or sacrifice creatures, because the Angel doesn’t interact with resolving spells or abilities at all.
Today’s Rules Tip written by
Josh Stansfield, Level 2 judge from Orange, CA