Way to go! The Big Bad's base is gone, his generals have been destroyed, and his Mooks have run away! It looks like you've finally won! Wait a minute, what's that crawling out from under the rubble? Yipes! It's the Big Bad, and he looks as mad as hell! What's this? He's challenging you to a final battle? Well, that shouldn't be too hard... unless. Oh Crap. He's pulling out all the stops! Prepare yourself for a Last Villain Stand!
This is where the Big Bad has lost his army, his plan has been ruined, and decides to fight the heroes on his own. Usually he uses Applied Phlebotinum or a MacGuffin to take on a One-Winged Angel form and becomes more powerful than ever before.
Usually, this is a desperate play by the villain when he has nothing left to lose, has gone through a Villainous Breakdown, and all that he's driven by now is a mad thirst for revenge for the heroes thwarting his plans to rule the world, the universe, or whatever he was after. He may take things to such an extreme that he doesn't care what happens to him as long as he destroys the good guys. It usually ends with the Big Bad being destroyed and the heroes coming out alive.
There are some cases where this trope is inverted when the Big Bad is a One-Man Army, his one man stand is not so desperate and he's still able to carry out his diabolical plans on his own. If this is the case, the villain is usually defeated when a miracle happens and the heroes gain the power needed to defeat him. This requires a certain amount of Villainous Valor, and if played correctly it may shift the audience's sympathy a bit more toward him.
Unlike a Last Breath Bullet, the villain is still very much alive. However, this can still lead to Taking You with Me. Compare with Last Stand, where it's the heroes who are the ones making the desperate play. Contrast with Villain Exit Stage Left, where the villain flees instead of staying to fight to the end.
Just about every villain in Digimon Adventure has one of these. In fact, the dub version of the episode were Piedmon, the literal Monster Clown, met his destruction was called "Piedmon's Last Jest". Of course, these examples could be considered inversions as they were able to successfully deal with the heroes only to be defeated when one of the members unlocked their digimon's newest evolution, thus giving them the strength to overpower the villains.
Frieza's last shot at Goku, in Dragon Ball Z, certainly counts. Frieza had lost all his minions, failed to obtain immortality, had been demonstrated as not being the strongest in the universe, had even been cut in half (by his own attack, no less), and was only alive because his enemy decided to give him enough energy to survive his injuries. Instead of using that energy to try to escape Namek before it exploded, he tries to kill Goku one last time.
He recovers though, albeit only for a time-traveling Trunks to effortlessly blast him and his father to pieces.
Megatron at the end of Transformers Cybertron. After he loses the Omega Lock, his minions have deserted him, and his plan to reshape the universe to his own desire is foiled, he decides to go all out and ruin the Autobots' plan to save the Jungle Planet for no logical reason while challenging Optimus Prime to a final battle.
During his final battle against Ichigo in Bleach, Grimmjow is sliced twice in the torso and stabbed in the heart but refuses to go down until he is sneak-attacked by Nnoitra
The Mobile Suit Gundam episode "Big Zam's Last Stand" serves as one for Dozle Zabi and the titular Big Zam. With his forces defeated by the Federation, Dozle sorties in the Big Zam, a prototype mobile armour, buying his troops enough time to retreat before he is killed by Amuro Ray. In the process he kills about half the Federation fleet, and nearly takes the Gundam with him.
The Anti-Monitor, multiple times during the Crisis on Infinite Earths. After his fortress and army get destroyed, he decides it's time to take on all the heroes by himself at the dawn of time. When this partially fails, he gets so angry that he essentially forgets his goal of multiversal conquest and concentrates solely on destroying Earth, slowly and painfully. And when that fails, and the heroes think him defeated, he clings to life through sheer force of will, multiple times, finally fighting a one-on-one duel in a weakened state with the original Superman.
The Great Mouse Detective: Big Bad Ratigan is utterly and completely defeated and Out-Gambitted - every single one of his options closed off by the heroes. He then resorts to attacking Basil head-on, with the singular intent of killing him.
In Mulan, Shan Yu after his army was wiped out by an avalanche and his generals have been captured.
He in fact does this twice: after losing most of his army, he and a small band of his most Badass henchmen come very close to victory anyway, and are prevented only by the Emperor's refusal to bow to him and Mulan's quick thinking. Following this, he tries to pull a Taking You with Me, and again comes very close to succeeding.
In Kung Fu Panda 2Lord Shen has his entire army destroyed, has killed his own Dragon, and lost everything. When Po finds him on the wreckage of his flagship in the middle of a Villainous Breakdown and offers him a Last-Second Chance. Shen rejects it and does the one thing he'd been running from the entire film, fight Po himself in a final showdown.
Auric Goldfinger escaped the destruction of his base, he cornered Bond and Pussy Galore on a plane to the White House, holding them up with a literal golden gun, only to miss his target and shoot a window before being sucked out of the plane and falling to his death.
His Stealth Yacht was burning but Elliot Carver from Tomorrow Never Dies still had a backup plan. Unfortunately after kicking Bond in the balls and holding him at gunpoint, he felt the need to explain this backup plan, giving Bond time to push him into the path of a whirling propellor thing.
In The Avengers, it becomes clear that Loki's entire plan is this to some extent; he already lost Asgard, the kingdom he actually wanted, in Thor, and so he tries to take the Earth instead, mainly to spite his brother. Before and during the final battle, Tony Stark explains at some length that "there is no version of this where you come out on top", Thor incredulously asks "You think this madness will end with your rule!?" and Loki doesn't actually refute what they say. On the contrary, there are several points throughout the film where it's made very clear that he sees no other option but to keep going, and the audience knows that he is being threatened with A Fate Worse Than Death if he fails to deliver the Tesseract to his mysterious benefactor, Thanos. Essentially, he knows that he'll almost certainly fail, but his pride won't let him surrender without trying every trick he can think of and it takes a hilariously one-sided confrontation with The Incredible Hulk to convince him that he really can't win.
Sauron at the end of the War of the Last Alliance; after losing most of his forces, he came out himself and faced both opposing leaders (Gil-Galad and Elendil) in a duel. He killed both of them, only to die himself (temporarily) when Elendil's son Isildur cut the One Ring off his hand. Subverted the previous time someone assaulted Sauron's fortress- when he realized that the Númenórean forces were too powerful for him to defeat, he came out to talk, not fight- and he ended up wrapping them around his little finger.
Hagen in the ending of the Nibelungenlied, because given that among other things he murdered Siegfried and Kriemhild's and Etzel's infant son, there should be no question that he is a villain.
The first Mistborn book has this, of the One-Man Army variety. Throughout the book, killing the Lord Ruler is treated as the most insane objective of an already impossible-seeming plan to overthrow The Empire. When the final stage of the plan is put into action, Vin meets the Lord Ruler face to face and realizes that yes, he can indeed still kick all their asses singlehandedly. The garrison is mostly absent; what's left has either defected or been defeated; the nobles are all hiding in their keeps if they haven't outright surrendered; and the order of dragons has been destroyed from within. But even as the resistance army Zerg Rushes the palace, the Lord Ruler decries them as beneath his notice. Somehow, Vin has to figure out how to kill him. Cue Final Boss battle.
Septimus Heap: Merrin Meredith's fight against Septimus in the river in Darke can be seen as this, since he's just lost his dragon and the control over the Darke Domaine and has barely anything to lose.
In Power Rangers Lost Galaxy, after Trakeena loses her entire army (though that was because she had them perform kamikaze tactics), her ship is destroyed, and all her minions are gone, she enters the cocoon her father made for her to take on the One-Winged Angel form she was destined for and in an act of pure desperation, powers up the remains of the Terra Venture and attempts to crash it into the planet the colony had flown to in an attempt to destroy them and the Power Rangers. She never even once considered that she would perish as well.
As stated in the quote above, Power Rangers Time Force has Ransik taking a last stand as well. It is inverted when he nearly wipes out the Rangers single-handed - he gets his visor blown off, but it ends up with just him and a demorphed, barely-standing Jen. He's only "defeated" when he attacks his own daughter by mistake, at which point he turns himself in.
In Power Rangers SPD, Emperor Gruumm ultimately takes a last stand as well. After his army is destroyed and Omni has fallen, Gruumm erupts from the rubble of Omni's mechnical body and challenges his nemesis Doggie Cruger to one last battle. When Doggie wins, Gruumm orders him to end it, but Doggie refuses, instead cutting his other horn off and arresting him.
Very common in the original Kamen Rider series. Many of the Generals/Commandants/Warlords, whatever they were called in their specific organization, would face down their Rider after he'd slaughtered their armies and ruined their plans enough, transform into a monstrous form with incredible power behind it, and fight the Riders one on one.
Happens by default in Kamen Rider Double, since Big BadJun Kazu/Utopia Dopant didn't actually have any minions or allies, and he's all that's left standing after original Big Bad Ryubee Sonozaki was defeated a couple of episodes before.
On Angel after her brainwashing powers are lost, Jasmine declares that if she can't rule the world she's going to destroy it. She shrugs off everything Angel tries to throw at her, but we don't get to see how she actually intends to accomplish her new goal because Connor, whose immunity to her powers apparently stretched to ignoring her invulnerability, shows up and kills her.
While every Mega Man boss is willing to hop in a mech or whip out a new battle body when you finally confront them, Epsilon of Mega Man X Command Mission is a little different in that he's fueled not by desperation, but by belief in his ideals and goal. He's also a little different in that he's not the Final Boss.
"I can see you are determined. But Scarface...I will not run from this fight. For I know that this bridge must be crossed to achieve our ideal. They will tremble before the power of...Epsilon!"
Minus the transformation (he did that earlier with some puppets) Ganondorf does the same thing at the end of The Wind Waker as the heavens actually the OCEANS rain down around them and Hyrule is lost to him forever.
And in Twilight Princess, after the Twilight has been purged from Hyrule and is unlikely to return, Zelda has been freed, and Hyrule Castle destroyed, Ganondorf does it again, first on horseback and then on foot.
Regardless of the above pattern, A Link to the Past provides an inversion, as the whole point of rescuing the maidens in the Dark World was to get Link into a position where he could kill Ganon before the latter could escape into the Light World. If the last fight was lost, Ganon would theoretically have been able to proceed with his plan.
Desann in Jedi Outcast still chooses to duke it out with Katarn, despite losing his entire fleet and most of his strike troops having been wiped out by the Jedi. Admittedly he doesn't even know the attack has failed until Kyle tells him just before the fight, and the entire thing was a diversion to get him to the Academy basement where the fight takes place anyway.
By the time you reach Colonel Autumn in Fallout 3, the Enclave has been utterly annihilated by your indestructible 40-foot tall super-robot, and all that's left of Autumn's army is him and his 2 bodyguards. Despite this, he proclaims that "the Enclave is at the height of its power!" and seems suicidally overconfident that he can take you, despite being a massively underpowered Zero-Effort Boss.
Mook example: Behemoth Kings in Final Fantasy XIII start off pretty strong, and when their HP gets down to half, they stand up. But it's when they're at under 10% HP that they're at their most dangerous: they'll start spamming Sunderevery few seconds! If you're not prepared for it, this will kill you then and there. (at this point it's easily enough to one-shot your Medic, and the battle is pretty much Unwinnable from there)
Araman pulls this in Neverwinter Nights 2: Mask of the Betrayer after you win your Crusade against the Fugue Plane. Considering you've killed him once already, and your party likely consists of four 30th-level characters, this qualifies him as Too Dumb to Live: one troper reported that he died the moment his speech ended.
Liquid Ocelot in Metal Gear Solid 4. Even after having most of his forces wiped out, from his Metal Gears being destroyed to his elite soldiers being essentially lobotomized after the destruction of the Patriots (long story), he still faces Snake in one final, climactic boss battle atop Outer Haven.
Liquid in Metal Gear Solid is another great example. After losing his standing army, all his allies and Metal Gear with no hope of attaining any of his initial objectives, he survives getting a missile to the face (the very same missile that ruined the super weapon on him). Assuming they are going to be hit by an air strike and die anyway he decides take out the frustration on Snake. He sets up an elaborate death trap to kill Snake's girlfriend involving a piece of dynamite, has a fist fight on top of the super weapon with Snake to prove his superiority (even though as previously stated he took a missile to the face, said missile was also strong enough to knock out Snake, the one who fired it). After Snake defeats him he seemingly falls to his death yet still manages to chase them in a machine gun car fight. Then after surviving a car crash he still crawls after Snake ready for murder. Only then does he finally die from a virus he received upon first coming into contact with Snake, meaning his entire encounter was one last stand even before losing everything else.
Dahau in Valkyria Chronicles III. He refuses to obey the peace treaty, and with what remains of his troops he activates a Valkyrian superweapon. In fact, in this battle he can't die even if you sic your Valkyria at him, you must deactivate the superweapon.
In Winx Club, near Valtor's end, he is humiliated by the Winx, loses most of the spells he stole, is abandoned by the Trix, and is nearly crushed by all the water of Lake Roccaluce. He survives and kidnaps the Specialists in order to lure the Winx to Andros and kill them with his last stolen spell, the Spell of the Elements. He ends up losing that and then loses control of his body to the Ancestral Witches before Bloom finishes him off.
Muammar Gaddafi planned to go out with a bang in his hometown of Sirte. Unfortunately things didn't go according to plan and during the battle he was driven into a sewer. When the rebels found him, his golden gun had run out of bullets. And then they proceeded tokill him.