The Bogo-Dutch

The Bogo-Dutch is a hypermodern defense to 1. d4 which is based on 1. d4 e6 2. c4 f5. It is a hybrid opening that is based on the Bogo-Indian Defense (1.d4 Nf6 2.c4 e6 3. Nf3 Bb4+) and the Dutch Defense (1.d4 f5).
Black tries their hardest to wrest control of the e4-square from White by checking on b4, plus having a pawn on f5 at the same time.
It is undoubtedly an underrated defense, to the point that most players, from super-GMs all the way down to amateur level, are completely unfamiliar with this entire set-up.