Nebula

Nebula, Gamora's sister, mutilated repeatedly by Thanos as a punishment for losing to Gamora in combat, begins a slow turn from villain to one of the most important characters in the saga. Mantis joins the team.

When does Nebula actually join? Not in these films. She's an antagonist in Guardians working for Ronan, and flies off at the end. In Vol. 2 she's hunting Gamora for revenge, then reconciles when Gamora explains she never wanted their father's contests either — and leaves again to hunt Thanos.

The survivors are: Rogers, Stark, Thor, Banner, Romanoff, Barton, Rhodey, Nebula, Rocket, Carol Danvers, Okoye, Pepper Potts, M'Baku, Wong, Happy Hogan — and Scott Lang, stranded and unaccounted for.

What are Nebula's neural links? Nebula is heavily cybernetic — Thanos replaced parts of her body each time she lost to Gamora in combat. Her systems are networked, which means the 2014 Nebula and the 2023 Nebula share memory access when in proximity.

In 2014, past-Nebula involuntarily accesses present-Nebula's memories and sees the Snap, Thanos's death, and the entire plan. Thanos extracts it from her. Past-Nebula then swaps places with present-Nebula and travels forward as a spy. Present-Nebula eventually kills her.

Didn't Thor already kill Thanos? Two different Thanoses. Thor killed the 2018 Thanos permanently at the start of the film. The one in the final battle is the 2014 version, pulled forward by Nebula's neural link — he has never snapped, never held the Stones, and is arguably more dangerous for it.

Guardians of the Galaxy Vol. 3 (FILM, 2023) — Rocket's origin: created by the High Evolutionary, who tortures and discards animals in pursuit of perfection. The team destroys him and frees his experiments. The team then disbands and reforms — Rocket becomes captain with Groot, Kraglin, Cosmo, Adam Warlock, and Phyla; Quill goes to Earth to meet his grandfather; Drax and Nebula stay on Knowhere raising rescued children; Mantis leaves to travel; Gamora returns to the Ravagers.