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What if Buffy never came to Sunnydale? Or Ryan Atwood, Newport Beach? Or even Clark Kent, Earth? The “What if?” question has become a staple television plot device, usually executed in the form of an “alternate reality” episode somewhere between the middle and end of a popular series. So it’s about right that Grey’s Anatomy, now halfway through its eighth season, has decided to take a stab at the question: what if Meredith’s mom never had Alzheimer’s? Here’s what we’ve gathered from tonight’s much-hyped previews: Meredith wears pink cardigans, Cristina has bangs, and Derek is now known as “McDreary.” We can’t wait to see what fun, wacky ways the alternate versions of the Seattle Grace staff collide. In the meantime, we invite you to click through our roundup of TV’s best “What if?” episodes and add your favorites in the comments.

Smallville: What if Superman didn’t exist?

We’d rather refer to Smallville’s “Apocalypse” episode as “Superheroes and Their Guilt Issues.” Clark wishes he had never existed, waxing about all the lives he’s ruined (seriously, can the guy focus on one good thing he’s done? Or at least have a beer?). Thankfully, the clone of his dead father, Jor-El, is around to knock some sense in him. He shows his son what life would be like if he had never been born, and it’s bad. Real bad. Lex Luthor is president. And he’s planning to nuke the world. Needless to say, when Clark returns to reality he decides to go back in time to Krypton to save himself as a baby (if you didn’t get that last part, just know it means he accepts his existence after all).