"It's sort of 'roid rage." That's how "Arrow" executive producer Marc Guggenheim describes the effects of the "mirakuru" drug to which Slade Wilson (Manu Bennett) was exposed on the remote island that, for a time, was the unforgiving home to him and Oliver Queen.

As you can see in the exclusive clip from Wednesday's episode of the CW drama (above), Wilson's fury over the murder of Shado by the nefarious Dr. Ivo has made Wilson far more intense than usual (which is saying something). That's partly the effect of the drug, which is a big part of the both the island timeline and present-day events in Starling City, where mirakuru is causing problems for Oliver's crime-fighting team.

According to Guggenheim, when the drug was introduced to the "Arrow" world, a lot of thought went into what its effects would be. The writers try to ground the more fanciful elements of Oliver's world in ways that make them feel like they "belong in the universe of our show," Guggenheim said. "We try to think of, 'What's the closest real-world analogue?' We let that be our compass -- that's what helps us keep the show grounded and not too science fiction-y," he said.

That's how the "Arrow" team came up with the real-world analogy of steroid abuse when depicting the effects of mirakuru, to which both Roy Harper and Slade Wilson have been exposed.

"It gives incredible strength, speed and endurance, but it also comes with cognitive impairment," Guggenheim said. The drug "draws out" anger, an emotion with which Roy (Colton Haynes) has already struggled at times.

"Things will get worse for Roy before they get better," Guggenheim said of the character's Season 2 storyline (Episode 12 will deal with Roy's challenges in more detail).

As Thea tries to understand what her boyfriend is going through, Oliver and his team continue to battle Brother Blood's attempts to create a mirakuru-enhanced army. As viewers learned in Episode 9, Slade Wilson is behind that project, although Oliver doesn't know that yet. So when will he learn the truth?

"We always do things sooner than anyone expects, but that said, as Slade alluded to at the end of Episode 9, it's been five years since they saw each other on the island," Guggenheim said. Wilson has spent that time coming up with an elaborate plan to deal with Oliver Queen, and Wilson is "playing a very long game."

As far as Wilson's concerned, "just killing Oliver is too simple and too merciful, quite frankly," Guggenheim said.

Of course, Slade Wilson and Brother Blood won't be the only foes who will face Oliver in the second half of the season. Michael Jai White will return as the Bronze Tiger, Robert Knepper will play the Clock King in Episode 14, and Katrina Law (like Bennett, another "Spartacus" alum) will play Ra's al Ghul's daughter, Nyssa al Ghul, in Episode 13.

And there are more personal struggles, too: In Wednesday's episode, Oliver and Felicity deal with the complicated repercussions of the accident that befell Barry Allen (Grant Gustin), the standout guest star of the last two "Arrow" episodes of 2013.

A pet peeve of the "Arrow" producers is a tendency among some shows to air backdoor pilots and then ignore the events of those episodes. The "Arrow" creative team was determined to make Barry Allen's impact on the characters a lasting one.

"We honor the relationship that Felicity formed with Barry, and we honor the emotional reaction to his accident," Guggenheim said. "It's not all swept under the rug."

Allen's introduction was very well received by critics and fans, and if all goes well, a "Flash" spinoff is possible for next fall -- though of course there's no official news on that front yet (if only the TV industry moved as quickly as the Flash!). And though Felicity and Oliver's reactions to Barry's accident are handled with typical finesse by Emily Bett Rickards and Stephen Amell in Wednesday's episode, as Season 2 progresses, the characters only have more problems to contend with. In fact, what Oliver will face in the second half of Season 2 will make his first-season struggles look easy by comparison, according to Guggenheim.

"His vow [not to kill] gets challenged by all the things he's facing. It's one thing for him to say he's a hero, but now he's called upon to really be a hero," Guggenheim said. "It's not just the no-killing code -- he's got to find a new gear and dig deeper and overcome tougher obstacles. He's got to bring people closer together and be more of a leader, even as that gets much harder. And on the other side of the board, Slade is manipulating events against him."

"The struggle for Oliver is," he added, "how does he adhere to the objective he set for himself of being a hero when things in the city start to get worse and worse?"