Wednesday’s episode is more than just a crossover event for “Arrow.” Season 5, episode 8 will, of course, feature characters from “The Flash,” “Supergirl” and “DC’s Legends of Tomorrow,” but it will also be the CW drama’s 100th episode. The milestone means that the hour will be extra special, and several spoilers for the episode have already been revealed.

The New World — Much of this episode will take place in a different reality. “Oliver (Stephen Amell) wakes up to a life where he never got on The Queen's Gambit,” the synopsis reveals. Oliver will notice that everything isn’t quite perfect, though.

Guest Cast — As previously reported, Oliver’s parents Robert (Jamey Sheridan) and Moira Queen (Susanna Thompson) are alive as is Laurel (guest star Katie Cassidy). Oliver is even about to marry her. Along with his loved ones being back, an enemy also returns. Deathstroke (Manu Bennett) will appear.

Not Everyone Is Back — Executive producer Marc Guggenheim explained that not every beloved character could return. “Colin Donnell is a series regular on a show. Colton Haynes had a lot of prior commitments,” Guggenheim told IGN. “We went in with a laundry list of things we wanted to see but at the end of the day, reality does at some point have to intrude. I think we came up with a clever way to have Colin and Colton represented, but it’s a challenge.”

Back In Reality — It looks like Oliver’s team will still be working while he is in dreamland. “Meanwhile, Felicity (Emily Bett Rickards) and the recruits take on a new threat with help from The Flash (Grant Gustin) and Supergirl (Melissa Benoist),” the synopsis reveals.

Oliver Draws A Line — The Green Arrow can believe in a lot of things, but aliens aren’t one of them. He won’t spend all of his time in the dream world. He’ll meet Supergirl in reality, but expecutive producer Andrew Kreisberg teased that he might not accept her.

“Part of Oliver’s journey in those episodes is he’s kind of hit his breaking point for things he’s willing to accept,” Kreisberg told Entertainment Weekly. “He’s had Mirakuru soldiers, the Lazarus Pit, magic, and Damien Darhk, but flying aliens who can incinerate you with their eyes is one beyond the pale for him. He’s keeping his distance, which is a very Oliver thing to do.”

Villains — Ollie is going to quickly trust Supergirl enough to work with her because they have a common enemy. Viewers will meet the Dominators on “The Flash,” and they’ll continue to cause trouble on “Arrow.” They’re aliens who want to destroy humanity, so obviously, it’s going to take a team of superheroes to stop them.

The 100th episode of “Arrow” airs Wednesday at 8 p.m. EST on The CW.