702.118b You choose which creature to sacrifice as you choose to pay a spell’s emerge cost (see rule 601.2b), and you sacrifice that creature as you pay the total cost (see rule 601.2h)
October 10, 2018 1:04 p.m.
Just for future reference, this site has a Rules Q&A section for questions regarding rules, cards, or card interactions. I've moved this thread over to there.
Unlike the regular forum section, the Rules Q&A section gives you the option of marking an answer as "accepted", signalling you no longer need assistance. This helps keep the forums a bit more organized by preventing answered questions from cluttering the homepage.
If you could please mark Skoodly's answer as accepted, that would be appreciated. Thanks!
October 10, 2018 1:24 p.m.
Please remember to mark the above answer as accepted so this can be removed from the unanswered queue