SPOILER WARNING: This article contains major spoilers for "Crossing Lines," the latest episode of Arrow.

Ricardo Diaz just got a lot more intimidating. In "Crossing Lines," the latest episode of Arrow, the returning super villain revealed he had created a serum that gave him enhanced strength and durability.

The episode saw Felicity continuing her quest for vengeance against Diaz and the Longbow Hunters. Using her technological know-how, she discovered he planned to break into the Center for Disease Control. She went to FBI Agent Samandra Watson for help and, though reluctant at first, Watson eventually joined Team Arrow's cause -- off the books, of course.

At the CDC, Felicity, Watson, Rene and Dinah went toe-to-toe with the Longbow Hunters. They soon found themselves outmatched and the Longbow Hunters made off with a vial. This failed mission also landed Watson in hot water; the FBI agent was subsequently assigned to desk duty in Washington, D.C., far away from the Diaz investigation.

Nevertheless, it wasn't a complete bust. Unbeknownst to Felicity, Rene had captured the Silencer. After Watson was sent away, he took Felicity to a warehouse, where he revealed to her that he had apprehended Silencer. He simply didn't want Dinah and Watson to know, as they were both insistent on following the rule of the law. Now, he and Felicity can question Silencer unimpeded.

As the episode drew to a close, it cut to Diaz's base of operations. There, he revealed he had several vials full of purple liquid. He subsequently injected himself with this liquid to show off its immediate effects. He punched a brick wall with his bare fist and it crumbled beneath the force. When he pulled his hand back, he revealed that this action hadn't cut or bruised his hand. As such, it looks like Diaz will be a much more formidable villain moving forward.

Of course, this move puts Diaz on equal footing with his compatriots Red Dart and Kodiak. After all, Red Dart has an arsenal of darts, each of which possess a different function, and wicked aim, while Kodiak displayed his superhuman strength and stamina in "The Longbow Hunters."

Airing Mondays at 8 pm ET/PT on The CW, Arrow stars Stephen Amell as Oliver Queen, David Ramsey as John Diggle, Emily Bett Rickards as Felicity Smoak, Rick Gonzalez as Wild Dog, Echo Kellum as Mr. Terrific, Juliana Harkavy as Black Canary, Colton Haynes as Arsenal, Kirk Acevedo as Diaz, and Katie Cassidy as Black Siren.