Dexter: Resurrection is not the first time that Dexter has been brought back to life, albeit the other times it wasn't as literal as it is this time. The original Showtime series ended in 2013 after an eight-season run, but the show made a comeback with Dexter: New Blood in 2021, and even that ended with Dexter literally being killed after being shot by Harrison.
So, when Dexter: Resurrection was announced, the first question on everyone's mind was, How is Dexter alive? The premiere episode for the show solves this mystery, and that too in the most Dexter-esque way possible. Dexter survived due to the cold climate. His heart rate was slow when he was shot, which helped in reducing the blood loss; hence, Dexter managed to survive.
Dexter's Resurrection in the premiere of Dexter: Resurrection

Apart from being a blood spatter analyst for the Miami Metro POlice Department, Dexter Morgan is a serial killer who hunts down people who, according to him, deserve to die. Dexter: New Blood ended with Dexter asking his grown-up son, Harrison, to kill him. The voiceover says, "Let me die so my son can live," while Dexter bleeds out in the snow and the series closes out.
Turns out, that was not the end for Dexter, even though showrunner Clyde Phillips did confirm in a conversation with Deadline that Dexter was indeed dead:
"I have three words for you: Dexter is dead...Here, there is no question that this is the finale of Dexter. Dexter is dead."
But in a later conversation with Variety, he hinted at how Dexter may have survived by adding:
"It's really cold out there"
The first few minutes of Dexter: Resurrection recap the events of the New Blood finale and reveal exactly how Dexter has managed to survive. It is revealed that Dexter was shot in extremely cold temperatures (0-degree degrees). The cold and the snow helped Dexter survive, and he's been admitted to the hospital, where he is unresponsive.
Dexter: Resurrection shows Dexter having suffered catastrophic blood loss and ending up in a coma for 10 weeks. The episode also finds Dexter seeing ghost-like visions of people from his past. The first vision is of Arthur Mitchell, who argues with him incessantly:
"But almost being killed by someone you’re fond of has its own particular sting, eh, Dexter?"
"Let me give you a little advice, serial killer to serial killer. Where you went wrong is thinking you could have it all —a family and your dark passenger. Like our savior, sometimes you have to go through hell to achieve resurrection. Not that we’re anything like the good Lord."
Arthur is followed by Miguel, his father Harry, and Sergeant Doakes as well. Nevertheless, Dexter wakes up from this blast from the past to find out what actually happened after he was shot by his son. He is informed how the cold temperature saved him and how he would have died already if he had been shot in the summer instead.

In a conversation with The Hollywood Reporter, Philips reveals exactly what led to this resurrection:
"When I wrote that [New Blood] finale —which was the most watched single episode in the history of Showtime, by the way —the internet went insane over it. Because they loved Dexter so much, and they love Michael Hall so much."
He added that Michael Hill agreed with the audience and wanted Dexter to be resurrected:
"Michael came back to me and said, ‘You know what, Dexter’s in my bones; Dexter’s in your bones, Clyde. Let’s keep going. Can you figure out a way to make it happen?’ And I did."
So, if everything goes well in the Dexter: Resurrection universe, this second, or, should we say, third, chance at life might last for multiple seasons.
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