The Superman Homepage has what appears to be a complete episode list and description of the entire Season One. My comments in italic.
Episode 1: "MAN OF TOMORROW"
When fearsome villains the Fatal Five set their sights on the newly formed Legion of Super Heroes, three of the Legion's members go back in time to get help from the greatest hero of all time: Superman. Instead they find Clark Kent, aware of his powers but not yet of his grand destiny.
The pilot episode.
Episode 2: "TIMBER WOLF"
A mysterious scientist asks the Legion to help capture a dangerous creature. They succeed, only to discover the creature is nowhere near as dangerous as the scientist himself.
Episode 3: "LEGACY"
Superman unknowingly saves the life of Alexis, one of the wealthiest people in the galaxy. Alexis and Superman become fast friends, but when Superman's Legion responsibilities get in the way of their friendship, Alexis decides to do something about it...
Maybe a Luthor thing. Can you have a Superman series without a Luthor?
Episode 4: "FEAR FACTORY"
During a cosmic storm, the team takes refuge in a creepy, derelict space station. On board, one-by-one, each Legionnaire faces his or her deepest fear -- and then disappears.
Episode 5: "CHAMPIONS"
While supporting Lighting Lad as he competes in the challenging Galactic Games, Superman and Phantom Girl uncover a sinister plot by the Fatal Five! Lightning Lad has troubles of his own when he finds his biggest competition from someone close to him.
Back in June, we learned that "Mekt Ranzz, Lightning Lad's brother, will appear in an episode." This sounds like it, unless it's Ayla here.
Episode 6: "PHANTOMS"
When Superman accidentally opens a gateway to a phantom dimension, a young man with powers identical to his is freed in the process. Now Superman must not only stop this destructive visitor, but also rescue the Legionnaires when they become trapped in the vistor's dimension.
Make way for Mon-el, stuck in the Phantom Zone!
Episode 7: "CHILD'S PLAY"
A young sorcerer arrives on Earth and causes a heap of trouble. In an effort to send him home, Superman learns of his vulnerability to magic, while Phantom Girl puts her diplomatic skills to the test as she travels to the sorcerer's secretive world to ask for help.
A "young sorcerer" could theoretically be Mordru.
Episode 8: "LIGHTING STORM"
Much to the Legion's disappointment, Lighting Lad accepts an invitation to join an older, "cooler" team. Once there, however, Lightning Lad realizes these new heroes aren't exactly what they seem. Now, caught between the Legion and his new friends, Lighting Lad must decide once and for all where his loyalties lie.
Episode 9: "BRAIN DRAIN"
A major malfunction sends Brainiac 5's genius IQ plummeting. To obtain the rare element needed to save him, Superman and Timber Wolf must travel to the most inhospitable planet in the galaxy -- and thanks to a transporter accident, they have only Brainy's head to guide them.
Episode 10: "THE SUBSTITUTES"
It's that time of year again -- Legion Auditions! This year's crop is hardly promising, with most hopefuls turning out to be comic duds. But when the Legion is overwhelmed fighting a mysterious foe in Earth's upper atmosphere, a group of rejects takes it upon themselves to save the world below... with outrageous results.
Holy crap! The Legion of Substitute Heroes! Legion rejects! Please have Arm-Fall-Off Boy.... I have a suspicion we'll see Ferro Lad in this batch - see the season finale for why.
Episode 11: "CHAIN OF COMMAND"
When disaster strikes Lightning Lad's home planet of Winath, the Legion is called to help. Lightning Lad's efforts to take charge are thwarted however when long-absent Legion leader Cosmic Boy arrives with an enigmatic new hero in tow.
At the San Diego panel, we were promised "familial Ranzz", so who's that with Cos here, Ayla?
Episode 12: "SUNDOWN, PT. 1"
The Legion is put to the ultimate test when an ancient weapon known as a Sun Eater comes to life. The Legion mounts a heroic defense, but the Sun Eater proves too powerful. Now at full strength, the unstoppable Sun Eater sets its sights on Earth...
Part one of a two-part episode
Episode 13: "SUNDOWN, PT. 2"
With the Sun Eater on a direct course for Earth's sun, the Legion has no choice but to ask bitter enemies for help to stop it. Superman meanwhile has his toughest battle yet when he discovers the stealthy alien controlling the sinister machine. In the end, the Legion triumphs... but at a terrible cost.
Part two of a two-part episode.
The Legion panel revealed that we'd see "Cosmic Boy for 3 episode arc at the end" so he must be in these two as well. I had figured we would not see the Sun-Eater saga - maybe Computo or Mordru instead - because of Ferro Lad. But what if he joins during tryouts in episode 10?