The buttons are listed in the splash in the beginning, and is listed as an NES controller- meaning as it stands right now, the game has only the standard buttons from the NES controller (A/B/Start/Select/Up/Down/Left/Right). The prompt saying "B" button is as it would be on an NES controller. Button mapping/etc is something that will be added further down the road, and as such prompts will only show the NES equivalent of the buttons (as shown in the intro splash).