How We Got Here: The episode starts with Agent Mulder being brought to the ER and he's dying.
Myth Arc: A very thrilling mythology episode with Shapeshifters, green blooded aliens, and a woman who claims she's Mulder's sister.
Shapeshifter Default Form: He looks very menacing. Fans nick-named him Schwarzen-alien as his actor bore an uncanny resemblance to Arnold Schwarzenegger.
Shapeshifting: The alien bounty hunter made his first appearance. He took the form of one federal agent whom he killed and used it to trick Agent Mulder. At the end of the episode, he forms himself into Mulder and tries to trick Scully. Had Mulder not been calling her, she wouldn't have recognized him as an imposter. This was one of the show's biggest ParanoiaFuels.
Super Window Jump: One of the clone doctors jumps from the fourth floor unharmed to escape the alien bounty hunter.
To Be Continued: First of a two-parter which ends up with Scully being attacked by Mulder's look-alike. And we know from the beginning of the episode that Mulder is dying!
The Un-Hug: Agent Mulder is called by his father to visit his mother due to a family emergency. When he arrives, Mulder greets him and goes for a hug. Bill Mulder, however, just extends his arm. They shake hands, but Mulder is visibly disappointed.