Apologetic Attacker: As Betts attacks the bar patron and later Scully, so that he can extract and consume their cancer tumors, he tells them both "I'm sorry... but you have something I need." He also apologizes to his colleague, as he kills her in a bid to keep his secret.
Body Horror: How Betts regenerates himself and grows a new body.
Car Fu: Leonard Betts tried to run Mulder and Scully over.
Chiaroscuro: It's noticeable especially in the scene in the storage locker where Betts gives birth to his another self. Beautifully and scarily lit.
Every Car Is a Pinto: Betts' retreating car blows up after Mulder and Scully each shoot one bullet in its general direction. Admittedly Betts was trying to fake his death, but there's no mention of the car being packed with fuel cans or something.
Faking the Dead: When Leonard Betts has a car accident, he has no other choice: after decapitation, he must pretend he died. He pulled this off as Albert Tanner. He tries to fake his death again after another accident.
Fingore: When Betts gets handcuffed to a car handle, he resorts to tearing off his own thumb. He does grow a new one, but it was obviously extremely painful.
Healing Factor: Leonard Betts is capable of very extreme regeneration of all body parts, including decapitated head. He can even create a whole new body. All he needs for his regeneration are human cancer tumours.
The Topic of Cancer: Leonard Betts eats and is made of cancer, plus it's revealed that Scully has developed cancer herself.
Waking Up at the Morgue: Even though Betts's head was decapitated, he was only mostly dead and woke up at the morgue. He waited when nobody was around and simply left. His head was alive, too.
Wham Line: Betts to Scully: "I'm sorry... but you've got something I need." A cancerous tumor.
Woobie, Destroyer of Worlds: Poor Leonard Betts. It's hardly his fault he needs to eat cancers, but his "death" put the hospital stores out of reach. In desperation he kills, and horrible though that is, until the accident he'd been just a really good (if occasionally cannibalistic) EMT.