Opening transpositions have a natural place in any player's repertoire, but I recently played a game which changed its name on almost every one of the initial moves. The game started 1.d4 Nf6 2.c4 e6, shown in the following diagram. I had the Black pieces and intended to play a Nimzo-Indian, 3.Nc3 Bb4, against my opponent who was rated about 200 points above me.
He headed on another course with 3.Nf3, a common reaction. Here I've played both 3...b6 and 3...d5, but I decided to steer into a Benoni with 3...c5, a system I like but generally avoid after 3.Nc3. I expected the standard 4.d5 exd5 5.cxd5, but my opponent dodged this with 4.Nc3. Although I've played this before, I don't know what it's called, assuming it even has a name. It's usually classified under ECO A32, which makes it a symmetrical English (1.c4 c5).
After the routine 4...cxd4 5.Nxd4, I continued 5...a6, tempting my opponent to steer away from my repertoire with 6.e4, which is exactly what he did. This is the same position that can be reached by 1.e4 c5 2.Nf3 e6 3.d4 cxd4 4.Nxd4 a6 5.c4 Nf6 6.Nc3 (ECO B41), a Sicilian with 2...e6. As noted in a post from last year, Will the Real Taimanov Please Stand Up, I recently added the 2...e6 Sicilian to my repertoire against 1.e4, where it has become my principal system of defense. I especially like its fluidity.
Although we soon reached a position that I had never seen before, I easily achieved a dynamic equality, and the game was eventually drawn by repetition after 30 moves or so. I know of a few other openings that switch between 1.d4 and 1.e4 systems, but there aren't many of them.