Welcome to Heaven
Missy was introduced as a mysterious character in Deep Breath. She is a recurring theme in Series Eight of Doctor Who welcoming people that have died into Heaven.
Missy was introduced as a mysterious character in Deep Breath. She is a recurring theme in Series Eight of Doctor Who welcoming people that have died into Heaven.

Half-Face Man is welcomed to the Promised Land by Missy

Gretchen was welcomed to Heaven by Missy

The Robots were heading for the Promised Land

CSO Matthew was welcomed to the afterlife by Seb

Missy says she has chosen well whilst watching Clara

The Doctor finds out who Missy is
Hello! I’m Missy, you made it. I hope my boyfriend wasn’t too mean to you. Missy

Missy was first seen in Deep Breath introducing people to the Promised Land/Heaven

Seb was first seen in The Caretaker interviewing someone in an office-like enviroment

Dr Chang works at the 3W believing the dead are still conscious
Some of the characters Missy could have been are shown below. In Dark Water she was revealed to be the Master.

The Rani

The Master

River Song

Clara

A member of the church
Welcome to Heaven Missy