Voltron has thwarted Sendak's conquest of Earth, only to be blindsided by the sudden arrival of a new and unknown mecha. Said new robot easily thwarts all of Voltron's and Atlas' attacks and defenses. When Voltron takes a direct hit from the mech, the paladins feel their energy being drained. A fight between the mechs ensues, but Voltron is eventually pinned down. Shiro somehow manages to convert the Atlas into a Humongous Mecha, which is able to fight the opponent on more equal footing, but they are still pinned down and drained of energy. Keith realizes that Voltron has to hit the mecha in the unarmored spot on its chest, and they are able to do so after another upgrade gives Voltron larger thrusters and a big sword.
When the dust settles, the mecha seems defeated. However, the paladins realize it is activating a Self-Destruct Mechanism, the blast radius of which will envelop half the planet. The team takes the mecha to space so the explosion won't hurt anyone but are caught in the explosion. The lions fall back to Earth.
Some time later, Shiro gives a speech at a Garrison funeral for the lives lost as the paladins recover in the hospital. Many of the paladins' allies have come to Earth, and the Voltron Coalition has extended aid to help rebuild it. Sam takes Allura to the mystery mecha's power source... which is apparently an Altean.
Tropes:
- Attack Its Weakpoint: Keith realizes that the only thing on the mecha that isn't armored is the portion on its chest that opens up when it's about to fire.
- Awesome, but Impractical: The Atlas Mecha is enormous, and fittingly powerful and tough, but as noted under Square-Cube Law below, the mystery mech is much faster and the Atlas spends much of the fight unable to connect.
- Aw, Look! They Really Do Love Each Other: When Keith wakes up after the battle, Kolivan, who usually treats him coldly, is seen smiling at him along with Krolia.
- Back for the Finale: The epilogue shows many of the show's minor/recurring characters moving to Earth.
- Bait-and-Switch: Shiro's speech after the Lions crash to Earth makes it seem as if all of the Paladins were killed, with the positioning of the Lions making it appear that he's speaking at his team's funeralnote . It's then shown that it's actually a funeral for the people killed during Sendak's invasion, and that the rest of the Paladins are recovering in the hospital while the Voltron Coalition sends aid to help rebuild Earth.
- The Bus Came Back:
- When Keith wakes up in the hospital, he sees that Kolivan and Krolia have come to Earth to see him.
- Several Balmerans, including Shay, come to Earth after the battle after not having been seen since season two.
- Matt Holt is seen coming home and reuniting with Pidge and his parents.
- Most of the figures from the coalition like Olia can be seen arriving on earth, as well as Veronica awkwardly shaking Slav's many hands.
- Call-Back: The Paladins note that their opponent's Quintessence-draining abilities resemble the Komar.
- Curb-Stomp Battle: The mystery mech completely dominates the fight against Voltron. Even when the Atlas transforms into a Humongous Mecha and joins the fight, the mystery mech still has the upper hand.
- Diabolus ex Nihilo: Nobody knows who sent the new mecha or where it came from.note
- Dual Wielding: Voltron gains twin swords to match the mysterious opponent.
- Grave-Marking Scene: After having recovered, Keith takes his mother to visit his father's grave.
- Hospital Epilogue: The ending scene shows the Paladins recovering from battle in hospital rooms surrounded by their respective loved ones.
- Heroic Sacrifice: Subverted. The Paladins seemingly sacrifice themselves to keep the mystery Robeast from destroying the Earth, but they turn out to have been injured rather than killed. When Shiro is giving his speech at the end, we see all of the Paladins recovering in the hospital with their loved ones.
- It Has Been an Honor: Keith says this to the other paladins just as they arrive into space, because at that point it was highly possible that they would die.
- Left Hanging: Haggar disappeared after Voltron's battle with Lotor at the end of the last season. No one knows where she is, not even her own druids. The Alteans originally freed by Lotor are mysteriously missing too.note
- Make My Monster Grow: The mystery mech is able to make itself grow to match the Atlas in size when attacking.
- Mana Drain: The mystery mech is able to drain quintessence from its opponent through physical contact, severely complicating fighting it.
- Relocating the Explosion: To protect the vulnerable Atlas, along with at least half the planet, from the mystery mech's imminent explosion, the Lions carry the mech into space where it won't hurt anyone.
- Repeat Cut: Voltron stabbing the mystery mecha gets three shots from different angles.
- The Reveal: Sam show Allura that the battery for the mecha wasn't a vial of quintessence, it was a female Altean.
- Rousing Speech: Shiro gives this during the memorial service for the fallen Garrison soldiers, as well as to a crowd of humans and aliens.
- Self-Destruct Mechanism: The mystery mech has one that activates when Voltron finally runs its core through with its sword.
- Series Fauxnale: Played with. The episode certainly feels like a Grand Finale to the viewer. The episode even has a number of tropes typical of a series finale. However, we know that there is still one season left. The discovery that an Altean was being used as a power source for the unknown mecha at the end also indicates there's more to come.
- Ship Tease: Shay hugs Hunk when she visits him in the hospital, and Acxa shows up to see Keith and Krolia at the grave of Keith's father.
- Square-Cube Law: The Atlas, when transformed, suffers from this. It is immensely powerful, but can't keep up with the far-smaller robotic foe.
- Transformation Sequence: Not for Voltron this time, for the Atlas, which transforms from a giant battleship into a mecha.
- Wham Shot:
- The Atlas converting itself into a Humongous Mecha that utterly dwarfs Voltron.
- The power source of the unknown mecha is revealed to be an Altean.
