Jarbear, the way I explained/understood essence transfer is as follows: essence transfer was a commonly known ability by the Sith, where you have to be killed while defenseless by a target harnessing the dark side for the transfer to succeed. But the form of essence transfer Palpatine learned is extra special, and it was originally discovered by Plagueis. I’d like to refer to it as premeditated essence transfer, where he is capable of expelling his own spirit and sending it into a dormant clone body from just about anywhere. And then obviously the Force ghosts hold his spirit in place at the end, effectively killing him.