The 2006-2013 couch gag is the ninth couch gag of Season 17.
The Simpson family sit on the couch as usual, but a camera flashes, setting off a series of family portraits that take place over the next seven years. In the 2006 and 2007 portraits, they all look the same, with the exception of the different arm positions of the family in 2007. In 2008, Homer is missing, Marge is wearing her black funeral clothes, and the kids are wearing their Sunday clothes. In 2009, Lenny has taken Homer's place and Bart and Lisa both begin puberty. In 2010, Carl has taken Marge's place, Lenny is still there, and Maggie is in different clothes and has given up her pacifier. In 2011, Marge is back, but has wrinkles under her eyes, Lenny is gone and is replaced by Jimbo Jones. In 2012, Homer is back, but is now a robot. Finally, in 2013, every member of the Simpson family is a robot.
Because of this couch gag being non-canon, the Simpson family actually didn't change like this between 2006 (Season 17) and 2013 (Season 25) due to the show being in a floating timeline (meaning that the family doesn't age, much less become robots).