Marvel Comics is teasing a big story coming later this year for Venom and the Symbiotes, with a full-page house ad appearing in this week's Empyre Magazine that reads "Knull is coming – 2020".
Knull is the evil god of the Symbiotes (alien beings known as the Klyntar that bond with host lifeforms, the most famous of which is Eddie Brock/Venom), an evil warrior deity who created the Klyntar and their rivals the Exolons as well as All-Black the Necrosword, an important artifact in the Thor mythos.
Known for killing other gods, Knull has played an important role in the background of writer Donny Cates's ongoing Venom run, with Cates also incorporating Knull into his Silver Surfer: Black limited series and Guardians of the Galaxy run. Though Knull's influence and machinations have been felt across those series – and Knull himself appeared in Silver Surfer: Black – the implication of this teaser is that Eddie Brock/Venom, and by extension the core Marvel Universe, will finally run afoul of Knull firsthand later this year.
Cates relaunched Venom in 2018, bringing in the concept of Knull and focusing on the relationships between Symbiotes – with his first major Venom crossover being 'Cult of Carnage'.
In the recently-released Venom #25, a two-page spread by artist Ryan Stegman (seen above) teased what was to come later - presumably whatever this 'Knull is coming - 2020' graphic is also referring to.
Prior to the release of Venom #25, Cates told Newsarama that the next story arc ('Beyond') will start the story on the path to Venom's "next big thing", while the upcoming Web of Venom: Wraith one-shot will be a "must-read" part of the story.