18-down works as follows: 2 down = BART, obovsuily. The likes of Bart = SONS and IMPS, which together make SIMPSONS. This was a bit nasty without an intuitive leap, as working through the clues in order requires understanding LISA as a synonym for daughter in 24-across. It's a bit of a circular reference, as you need to have LISA to get MAGGIE for 3-down, which then gives BART for 2-down, and thus SIMPSONS for 18-down.Or, of course, you could stare at ____ | G_O_____ for long enough to see that it's Matt Groening, which is what both I and AS appear to have done.