almost definitely a lesser known character called KGBeast given they have the same name. How the show goes from here to there is a big ? though.

Teen Titans are a teenage super-hero group. Been around since the 60's, in the beginning consisted entirely of sidekicks. The following all originated as Teen Titan villains: Deathstroke, Brother Blood, H.I.V.E.

The Suicide Squad are a government special ops team comprised mostly of super-villians who are essentially doing "community service" (ie; participating in missions in return for reduced sentences). Amanda Waller serves a similar capacity as Nick Fury. Bronze Tiger and Deadshot are both members with Deadshot and Captain Boomerang aka George "Digger" Harkness being two of the higher profile members.

The Secret Six were originally a covert team (non-superhero) organized by Mockingbird who blackmailed the participants into taking on missions (ie; similar to the Suicide Squad). This later became a villain team spin-off/similar to the Suicide Squad (or Marvel's Thunderbolts) and included Deadshot.

The League of Assassins is Ra's al Ghul's organisation. Bronze Tiger was a member for a while. They have a ton of history with characters like Batman - But you've all seen the Nolan Batman movies I'm sure which do a pretty good job on the back story.

Nanda Parbat is a Utopian fictional city that is periodically under siege by the League of Assassins. It's most notable for Deadman which I can't see Arrow using. But it has exciting implications if they do.

Professor Ivo is one of DC's many mad scientists. He's most known for the constant pursuit of immortality (usually resulting in really bad side effects for himself) and the creation of Justice League super-villain Amazo. (Using Amazo would be really strange unless very long term planning going on here [Justice League] so only reason to use Ivo instead of one of a dozen other characters is crazy pursuit of immortality)

S.T.A.R. Labs is a pervasive research group used throughout DC comics though most associated with Superman. Though Cyborg of the Teen Titans and Justice League was created as a result of a S.T.A.R. Labs incident. Due to the Law of Conservation of Detail if Arrow were to ever go down those routes I could see them working in similar themse and characters like Flash, Firestorm or Project Cadmus into S.T.A.R.