Not only is the season 2 finale of "Arrow" going to be explosive, but it will feature a blast from the past from surprising faces and the ultimate showdown between Oliver Queen and Deathstroke.

In the last episode, Starling City was under attack by Slade's Mirakuru army. Although S.T.A.R. Labs finished its Mirakuru cure, Slade's men recovered it before Team Arrow could get their hands on it. Sebastian Blood, however, realized that Oliver's warning about Slade was true and put his life on the line to steal the cure and give it to Oliver, which resulted in his death, Hypable.com reported.

Meanwhile, Sara returned and reconciled with her sister Laurel. Plus, A.R.G.U.S. sent troops to barricade Starling City to prevent the Mirakuru soldiers from escaping. When the episode ended, Amanda Waller gave Oliver until dawn to somehow apply the cure stop Slade or a drone would level the city.

At least two members of the Suicide Squad, Floyd Lawton, aka Deadshot, and Lyla, will return in the upcoming episode, "Unthinkable." They will team up with Team Arrow to try to stop Deathstroke's army of super-soldiers. Oliver will also try to stop Slade from purposefully killing another one of his loved ones.

In the meantime, a confrontation will develop between Diggle and Amanda Waller, who plans to blow up Starling City in order to isolate Slade's army, CarterMatt.com reported.

According to ScreenCrush.com, "Arrow" released 25 new photos from the finale, featuring shots of Amanda Waller, Deadshot, Diggle, Lyla and the rest of A.R.G.U.S. In other photo, Slade looks like he is forcing Oliver to choose to kill either Felicity or Laurel. Another picture shows Sara taking on Summer Glau's Isabel Rochev/Ravager in the Queen Consolidated offices, while it seems like Nyssa al Ghul and the League of Assassins come to the rescue. Roy Harper is also featured in a pic wearing a red domino mask.

The CW released a synopsis of the "Unthinkable" that states:

"Slade (Manu Bennett) moves forward with his plan to kill one more person in Oliver's (Stephen Amell) life. While Oliver has fought all year to be more than the killer he once was, when Slade kidnaps someone close to Oliver's heart, Oliver is pushed to the edge and realizes sometimes it takes doing the unthinkable to stop the monster.

"Meanwhile, Diggle (David Ramsey) takes on Amanda Waller (guest star Cynthia Addai-Robinson) with a little help from some friends, and Thea (Willa Holland) turns to Roy (Colton Haynes) in her time of need."

In an interview with The Hollywood Reporter, actor Michael Rowe dropped a few spoilers hinting at what's to come in the big finale and the role that his character Deadshot will play. According to him, Diggle beseeched his arch nemesis for help in order to stop Slade's army.

"Diggle takes this on and he needs some help, so guess what? He calls his buddy Deadshot," Rowe said. "It's the most unlikely duo having each other's backs and neither one trusting each other a lot but certainly makes for good storytelling."

The actor also promised that the finale will take fans on "a wild ride," adding that after a "big, catastrophic event, all the shrapnel ... that spin off of that, you're not even going to understand the things to come."

"It's worth the wait. Everything is addressed in this final episode. It's epic -- they went so huge with it," Rowe said. "But in the midst of tying up these loose ends, it's setting up season three. People are not going to be disappointed."

"Arrow" S2E23, "Unthinkable," airs Wednesday, May 14, at 8 p.m. EDT on The CW.

Watch the official trailer below.