I Gotta Get Some Air

Titan reluctantly meets his old boss Machine Head and learns that Mr. Liu, the dragon's human host he thought dead, survived and now hunts him for revenge. Machine Head dangles a return to The Order and its protections, but Titan refuses to surrender his hard-won independence. At the Global Defense Agency, Cecil and Donald fret over Mark's growing willingness to kill, while at the Guardians' headquarters the team fractures over his execution of Sequid host Rus Livingston. The tension turns real when Rudy coughs up a live Sequid hidden in his stomach, and Monster Girl crushes the parasite before it can seize his mind, leaving Rudy convinced their enemies will only keep returning stronger.

Mark, haunted by the killing, cannot reach Eve, whose transmutation powers keep dissolving into useless mush. When Magnattack, a ferrokinetic assassin hired by Mr. Liu, slaughters Titan's guards in a park, Titan shifts to stone to shield his family and beats the killer to death. The violence rattles everyone, and Cecil's praise of Sinclair and the ReAnimen only drives a disgusted Mark to storm off.

Too drained to answer Titan's call for help, Mark delegates the job to his exhausted brother Oliver, now operating as Kid Omni-Man. The Flaxans then launch a massive fourth invasion, armed with advanced Mini-Mecha and a temporal field generator that keeps their soldiers from aging on Earth. Rudy pinpoints the emitter inside the Flaxan dimension, defies Cecil's orders, and charges through the portal to destroy it, collapsing the invasion. Resolving to dismantle the Flaxan empire from within, Rudy and Monster Girl choose to stay behind, and the gateway snaps shut, trapping them in the hostile dimension.

Mark rushes to aid Oliver against Mr. Liu, who has transformed into a colossal dragon, and vents his rage to force the villain into retreat. Misreading the situation as Titan endangering his little brother, Mark turns on him with a savage, near-lethal beating that mirrors the one Titan gave Magnattack, stopping only when a horrified Oliver screams at him.

Debbie patches up Oliver at home while Eve reveals that Rex found nothing wrong with her fading powers. A broken Titan returns to Machine Head to rejoin The Order, only to discover Mr. Liu already seated at the table under a new profit-focused truce. That night Mark jolts awake in a panic and finds Eve in the bathroom, silently staring at a positive pregnancy test. The third episode of the fourth season, and the twenty-seventh overall, it brings the Flaxans back for a fourth attempt on Earth, formally inducts Oliver into Invincible Inc., and takes its title from an issue of the comic.