Which symbiotic characters were introduced in the two-part episode of Spider-Man? 
Spider-Man: The Venom Saga:  These certain episodes are responsible for debuting the symbiotic characters Venom and Carnage outside of comic books. Symbiote (comics): The Symbiotes (originally known as the Klyntar) are a fictional race of amorphous extraterrestrial symbiotes appearing in American comic books published by Marvel Comics.
Venom and Carnage