Reversed Mokele Mbembe

After 1. d4 e5 2. Nf3 e4, the advance known as the Reversed Krebs, White must move the attacked knight. With 3. Ne5 it goes forward rather than back to g1, which would be the Reversed Brooklyn. The square looks active, but the knight has no pawn support and no secure retreat, so Black can harass it while developing. Reference sources treat the move as dubious, because each time the knight is driven off White loses another tempo.

The two main replies are almost equally common. 3...d5 occupies the center and backs up the e4-pawn, leaving the knight on e5 for the moment. 3...d6 challenges it at once. After 3...d6 4. Nc4 d5, the knight is pushed back again and Black has a comfortable position with a broad pawn front. A smaller group of players chooses 3...f6, which also attacks the knight. The engine's first choice is 3...c6, ahead of 3...d6 and 3...d5, and it rates Black's position as slightly better. In online games Black scores better than White, and the line is a rare guest in serious play.