The man turned up uninvited at the Christchurch funeral for 90-year-old Harold Ritchie on Wednesday, banged on the coffin and told the deceased to "wake up''.
He had called the family through last night and asked to meet them at Mr Ritchie's grave at 11am today.
The disturbing saga involving the mystery man began at Mr Ritchie's funeral at John Rhind Chapel in Richmond on Wednesday.
About 80 minutes into the service a man aged about 20, wearing a suit, walked up with a prayer book in his hands and began shaking the hands of family members.
No one questioned him because it was thought he knew Mr Ritchie.
He then went to the coffin and began chanting with his back to the mourners.
Mr Ritchie's daughter, Jeanne Kiddie said: "He put his arms up in the air and he seemed to shudder, like he was vibrating. He was shouting in tongues.
"He picked up the photo of dad from the coffin and studied it for a while. Then he went down on his knees and shouted "Wake up Harold!" and thumped on the casket.
"I was horrified, absolutely horrified."
For a moment Mrs Kiddie, who was stunned, thought the mystery man was about to try to open the casket.
The man left after being spoken to by family.
Mrs Kiddie's husband, Ross, said the man's phone call last night had been another blow to the family.
"We're really shattered now. We were saying we could probably get through it, we could pick ourselves up, move on, and we were getting to the stage where we said we weren't going to talk about it so much."
During this morning's phone call, the man said he believes the reason Mr Ritchie did not wake during the funeral chant was because he called him Harold.
Mr Ritchie's birth name is Malcolm, but he was known as Harold.