I'm pretty sure Smallville has Clark Kent and and alternate universe Clark Luthor in the later seasons, though I didn't watch, so I can't tell you when that happened.
the SPN eps referenced above: in Dream a Little Dream, there's Dean & demon!Dean, in Skin, there's Dean and shapeshifter!Dean, and in The End there's Dean and future!Dean.
The Dark Angel ep with Max and her clone is She Ain't Heavy. Alec and Ben never interact, but the Ben episode is Pollo Loco, and the episode with Alec in the present and Ben in flashbacks is Hello Goodbye.
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the SPN eps referenced above: in Dream a Little Dream, there's Dean & demon!Dean, in Skin, there's Dean and shapeshifter!Dean, and in The End there's Dean and future!Dean.
The Dark Angel ep with Max and her clone is She Ain't Heavy. Alec and Ben never interact, but the Ben episode is Pollo Loco, and the episode with Alec in the present and Ben in flashbacks is Hello Goodbye.