Ant-Man

Scott Lang, a burglar fresh out of prison, is recruited by Hank Pym to steal a shrinking suit before Pym's protégé Darren Cross can weaponise the technology. Lang succeeds, goes subatomic to sabotage Cross, and — critically — returns from the Quantum Realm, which Pym had believed impossible. That single fact is the seed of Endgame's entire solution.

Darren Cross has spent years reverse-engineering Pym's shrinking formula into the Yellowjacket suit, and has been selling it to HYDRA. The heist is a heist: Lang, Hank, Hope and a crew of Scott's former cellmates break into Pym Technologies to steal the suit and destroy the research.

The finale is fought at a scale-shifting comedy of a size — a toy train set, a briefcase, an ant named Ant-ony — before Lang shrinks between the molecules of Cross's suit to sabotage it. Doing so takes him past the subatomic limit, into the Quantum Realm, and he comes back by overriding his regulator. Hank had believed that impossible for thirty years, and that single fact is what Endgame is built on.