Plot hole: After Rita kills Billy, why didn't any of the other rangers do something to help him? They could have very easily done CPR on him or at least called for an ambulance.
Suggested correction: (1) they did...they took him to Zordon. (2) These are high school kids. Have you ever seen any slasher flick before? Not every HS kid knows CPR.
Every high school lifeguard that ever existed.
Suggested correction: They may have not been in range with cellphone towers to get a good enough signal. Also, they had superpowers including super strength so doing CPR on Billy would have been very dangerous and would have probably hurt him even more.