The villain, who never had any intention of letting the hero (or heroes) live, has finally instituted the perfect plan that will ensure their demise (or at least, that's what the villain thinks). Of course, for some people it's not enough to simply kill the heroes. They have to crush their hopes utterly, ensuring maximum despair and humiliation. In short, they have to tell them death is inevitable. This is never wise.
A form of Evil Gloating; this tends to be standard for a Smug Snake. Expect this to almost always be invoked when there's a Death Trap. The villain can and will combine this with "The Reason You Suck" Speech.
This would be a Stock Phrase... although very few villains end up saying this the same way twice. The classic villain threat has several variations, some of which are:
The Wizard of Oz: The Wicked Witch hands Dorothy a large hourglass and tells her this is how much time she has left to live. It's actually how much time before the Wicked Witch gets back and kills her.
Parodied/referenced in Flash Gordon: "You have until the sands... run up."
Star Wars: The page quote, in response to an unusual turnabout given by Luke.
Interestingly, the page quote is actually Palpatine talking about the Rebels, not about Luke himself. It's only after Luke refuses to join the Dark Side that Palpatine repeats the trope on Luke specifically. And he would have been right if it hadn't been for Vader'sHeel-Face Turn.
"So be it, Jedi. If you will not be turned, you will be ... destroyed!"
"And now, young Skywalker ... you will die."
Blade Runner: Tyrell's immortal "revel in your time" line may be this trope.
Herald: By noon this day, you will be dead men. The thousand nations of the Persian Empire descend upon you! Our arrows... will blot out the sun! Stelios:Then we will fight in the shade.
In Flash Gordon, Flash is due to be executed, but is given a few minutes to see his girlfriend one more time. The Dragon puts a big hourglass in the room so they know how little time they have left.
In Alien, Ash's last words before being incinerated were "I can't lie to you about your chances, but... you have my sympathies."
Darkness Visible has an unusual example because, rather than the hero being at the villain's mercy, the villain is actually chained to a prison wall. However, his Evil Plan is still in motion, leading to this variant on the threat:
'I have taken away your need to fear growing old. You will not be thirty for very long!'...'You cannot stop it, Henry! You can only fail and die, and I hope you die with the knowledge that you lost at the forefront of your mind!'
Artemis Fowl has this when Opal captures Holly and Root, then ties an explosive to Root, giving him at most a minute to live.
This time the evil plan actually works. Root blows up.
In the Left Behind book Desecration, when Buck Williams and Chaim Rosenzweig (as Chaim the prophet) are about to leave the Knesset after Nicolae Carpathia negotiates with them for a lifting of the plague of sores from the First Bowl Judgment, Carpathia threatens them with "Your days are numbered". In the Dramatic Audio version, Buck's retort to Nicolae, "As are yours, 'my friend'," is a warning that what God's Word says about him will come to pass.
You need not fear us, unless you are a Darkheart, a vile one who preys on the innocent. I promise: you can't hide forever from the empty darkness, for we will hunt you down like the animals you are, and pull you into the very bowels of Hell!
You at the barricade listen to this! No one is coming to help you fight, you're on your own, you have nofriends, Give up, your guns OR DIE!You at the barricade listen to this! The people of Paris sleep in their beds! You have NO CHANCE, NO CHANCE AT ALL!Why throw your lives away?
Sovereign:We impose order on the chaos of organic evolution. You exist because we allow it, and you will end because we demand it.
Harbinger:Human, you've changed nothing. Your species has attracted the attention of those infinitely your greater; that which you know as "Reapers" are your salvation through destruction.
Reaper: Every organic civilization must be harvested in order to bring order to the chaos. It is inevitable.
Turns out that the Catalyst who created the Reapers is fond of this. He claims that if Shepard chooses Destroy, which will wipe out all synthetic life in the Galaxy, because their body relies on cybernetic implants to survive, Shepard will die alongside the Reapers. Shepard can respond by blasting the crap out of the Power Conduit anyway, with a look on their face that clearly says they are intent on Taking You with Me. With a high enough EMS score, Shepard is seen taking a breath in the rubble, implying that they did manage to survive after all.
In Transformers: War for Cybertron, Trypticon's last words to the Autobots are: "You haven't defeated me Autobots!" Optimus promptly uses his axe to knock him into a pool of energon. As the next game would show, Trypticon's body would not recover and would be permanently converted into the Nemesis.