It’s confirmed Palpatine was using Vader’s voice to talk to Kylo through the force via the broken helmet, which I think the visual dictionary says Palpatine cursed it before his fall in ROTJ, Is there anyway of showing that better in TROS/TLJ/TFA, felt very foggy and left out.

Would be interesting if Vader said ‘Find Me’ instead of Palpatine at start of film - He used Vader’s voice to create a fake sense of security in controlling Kylo, he actually believed Vader’s spirit was guiding him.