In this episode Lex wears a kryptonite ring to stop Clark from using his powers to stop him. In the comics Lex Luthor always wore a kryptonite ring to ward off Superman, and it eventually led to him getting cancer from the constant radiation of the kryptonite.
This is the first time Lionel Luthor is seen back in his signature look (black suit and overcoat) since the penultimate episode of Season 3. Of course, this coincides with Lionel's return-to-form at the end of this episode as he exclaims "we're Luthors" to his son.
When Evil Lex gives his monologue about joining him and ruling the world, he says, "I want you to remember this day, Clark. I want you to remember that, despite all your amazing powers, there was one man that beat you." This parallels a famous monologue of Bruce Wayne/Batman in the famous Dark Knight Returns, where he says, "I want you to remember Clark, in all the years to come, in your most private moments, I want you to remember my hand at your throat. I want you to remember... The one man who beat you."
Michael Rosenbaum tells the story at panels that he had told Tom Welling he should have been paid twice for this episode since he played "two characters." Tom laughs back that that is not how it works.
"Evil Lex" challenges Lionel to a fencing duel in order to see whether Lionel is still worthy to be his father. This is reminiscent of the duel in which Lionel challenged Lex in on "Hothead".