My opponent cast a big thing and put the return trigger on the stack. They then chose to exile return and it immediately did damage to my board without giving me a chance to respond.
Tag applied: Could Not Reproduce Testing applied: Game state reproduction with and without No Possible Move: Yield All activated. Test Results: Priority was give to the user with Saffi Eriksdotter and was able to activates it ability before Kozilek's Return resolves from the stack.