Judge McKenzie said his list of convictions, especially over the past two years, had shocked her.
"All have a common thread or theme, which is violence-related.
"When I was reading the police summary of facts, what struck me was that all these incidents appear not only to be serious but unprovoked and random."
She said the lead offence was the firearms charges. They related to an incident where he pulled out an air pistol from his pocket, while a group of 15 and 16-year-olds were walking towards him in Koutu. He pointed it towards a teenage girl.
According to the summary of facts, Mellow said nothing to the girl but continued pointing it at her causing her to believe she was going to be shot.
"She yelled out to him to calm down, at which point he walked off holding the pistol in his hand and went into his home address."
The group ran off and police were called. The area was cordoned off and armed police tracked Mellow down.
"The victim was not injured in this incident but believed she was going to die. It took her some time to calm down and talk to police," the summary said.
Judge McKenzie said Mellow had pointed the gun "at the head of a 15-year-old girl that was unknown to you".
In relation to the assault charge, Mellow started to argue with his brother while they were sitting on a public bench on August 4. He then punched his brother at the back of the head before punching him in the face.
"Your brother suffered injuries as a result," Judge McKenzie said.
A probation report described Mellow a high-risk of re-offending. "You need to grow up, start taking some responsibility and deal with what clearly is a very clear problem ... violence and anger."
