Here is my prediction for the main cast for Season 10:
Tom Welling as Clark Kent
Allison Mack as Chloe Sullivan (Episodes 1-5)
Erica Durance as Lois Lane
Cassidy Freeman as Tess Mercer
Justin Hartley as Oliver Queen
Annette O'Toole as Martha Kent
Michael McKean as Perry White
Recurring Roles
Callum Blue as Zod
Zod manages to escape punishment on New Krypton and decides to return to Earth to exact his revenge on Kal-El for ruining his idea for Earth and for turning his own troops against him. He kidnaps Kal-El's best friend and his girlfriend, sadly he kills Chloe Sullivan before he in turn is killed by Oliver Queen using a Kryptonite arrow in the back of the head. (Episodes 4&5)
Unknown as Granny Goodness
Darkseid's agent on Earth working alongside Intergang in search of the Anti-Life Equation. She used a Mother Box on Tess Mercer and recruited her to help her find the Anit-Life Equation, coming face to face with Clark Kent when her methods are questionable. (8 Episodes)
Matt Morgan as Darkseid
(He was due to play Doomsday if the story went into Season 9) Darkseid, the powerful dictator of the planet Apokolips sends his agents across the universe in search of the Anti-Life Equation and when his earth agent reports back with good news, he launches a full scale search of the planet, coming head to head with Earth's protectors, the Justice League led by Clark Kent. (4 Episodes)
Glen Jacobs as Kalibak
The first son of Darkseid, he is abused by his father who takes advantage of his son's need to prove himself by sending him to earth to assist Granny Goodness in their search for the Anti Life Equation, where the two rivals search to seek Darkseid's approval.(6 Episodes)
Alessandro Juliani as Emil Hamilton
On hand to assist the Justice League, when Watchtower dies at the hands of Zod, Hamilton is needed even more and try and bring back the estranged Justice League who have drifted apart since the death of Chloe Sullivan. (5 Episodes)
Alaina Huffman as Dinah Lance
Dinah Lance is the alter ego of the Black Canary member of the emerging Justice League. (2 Episodes)
Kyle Gallner as Bart Allen
Bart Allen, aka Impulse of the Justice League is the hothead of the team. (2 Episodes)
Phil Morris as J'onn J'onzz/John Jones
The last of the Martian's, John is still a Police Detective in Metropolis and is an active member of the Justice League. After the death of Watchtower, John takes a more active role with the Justice League behind the scenes at Watchtower to replace Chloe, trying to bring back the Justice League members who have drifted apart.
Below are Season story arcs:
Clark Kent
After sacrificing himself to send Zod away, Clark is taken to Met Gen with stabs wounds and is exposed as being super-powered despite Emil trying to persuade the other staff otherwise. This leads Clark to believe he needs an improved identity as "Clark Kent" and begins to wear glasses more and more. He also has to convince Lois that he and the "Blur" aren't the same person, as she is on a constant quest for the truth that begins to drive a wedge in their relationship. He must also deal with the death of Chloe at the hands of Zod who returns and is ultimately killed by Oliver in revenge, which forces Clark to abandon Oliver. Clark is also trying to deal with the emerging threat from the New Gods, Granny Goodness and the greater threat of Darkseid who is in search of the Anti-Life Equation, using Intergang's resources on Earth to help his search, a story that as "Clark Kent", he and Lois are pursuing for a major storyline for the new Editor in Chief, Perry White.
Chloe Sullivan
After rescuing Oliver from Intergang after he was kidnapped, Chloe's life is almost perfect, until Zod returns from New Krypton and kidnaps her, as bait for Clark who seeks revenge on. Chloe is caught in the crossfire and is killed by Zod, burning her alive.
Lois Lane
After believing that Clark is the Blur, Lois begins a quest to find out the truth. She begins to try and expose Clark as the Blur by getting herself into trouble with Intergang, but Clark saves her not the Blur. She is convinced for now but is still suspicious and along with Clark as her partner, try and expose Intergang and their connection with aliens for a major story to catapult her into a star reporter, trying to impress Perry White, the new Chief.
Tess Mercer
After dying from severe burns at the hands of Zod, she is brought back to life by Granny Goodness, an agent of Darkseid from Apokolips who is searching for the Anti-Life Equation. She is forced to work for Granny who is using Intergang to help her search the globe. After losing LuthorCorp after she was announced dead, Tess is on her last limb and trying to make amends for herself after nearly helping the Kandorians take over the earth, determined to not make the same mistake by helping Darkseid to save Earth.
Oliver Queen
After being kidnapped by Parademons and taken to Intergang's base, he is broken out by the Justice League. After reuniting with Chloe, life is back to normal for Oliver until Zod returns from New Krypton and burns Chloe to death, forcing Oliver to kill Zod with a Kryptonite arrow to the head, forcing Clark to abandon Oliver and putting a wedge that seems unbreakable between them. Oliver sinks back into a slum and seperates himself from the Justice League, deciding he works alone, occasionally working with them when necessary.
Martha Kent
After Perry gets the job as the new Editor in Chief, she moves back to Smallville to be with him and also to keep a close eye on Clark to ensure he fulfills his true potential as a hero. Things are rough between her and Perry as Perry is simply not Jonathan and they soon break up. After Martha becomes aware of the threat that Darkseid, Granny Goodness and Intergang pose, she begins working with John Jones after the Justice League split up after Chloe's death, to stop the threat that may cause Clark any harm.
Perry White
When Perry gets the job as the new Editor in Chief, he moves back to Metropolis permanently and asks Martha to move with him. When she decides to stay in Smallville, they make the decision to break up and Perry digs himself in work. He tasks Lois and Clark to tap into their full potential and get the story of a lifetime. As they do that, Perry is determined to get the story on Intergang and expose them, clashing with Lois and Clark's story.
Darkseid
The main "Big Bad" will be Darkseid, but he is teased throughout the season and is only seen briefly in a teaser in episode 5 and again in episode 11. He is then on full view in Episodes 21 & 22. He is searching for the Anti-Life Equation and believes it is on Earth. He has already sent Granny Goodness ahead and soon sends Kalibak to assist when word of the presence of Clark Kent and the Justice League provide stumbling blocks. When they continue to disrupt his plans, he goes to Earth himself with an army of Para-demons behind him to finally put an end to the Kryptonian.
Other notes
Bruno "Ugly" Manheim will return as a recurring character.
Clark is evolving his "suit" throughout the season, wearing the "Blue T-Shirt" that was given to him by Martha initially. In the finally
Episode 4 is the 200th episode, which is when Zod returns and kills Chloe.
Episode 11, the Legion of Super-Heroes returns written by Geoff Johns. This episode will feature Darkseid.
Clark wears the glass more in this season, in the final 3 episodes he wears them full time. Throughout the season, he wears them occasionally.
In the SERIES FINALE, Oliver returns from his self exile and helps Clark defeat Darkseid. He then says that he isn't staying and is returning to Star City because too many bad memories are in Metropolis.
The real Jimmy Olsen goes into Perry White's office with an application form as an intern, though we only see the back of his head.
Clark finally puts on the suit and we see him in it, this is the final shot of the series.