The dash between Beppi's Donkey and the cart with the dolls in the left side of the screen is frame perfect? (without smoke bomb i mean)

Actually, It doesn't have to be. As long as the donkey doesn't go into its green phase, you can dash in between the donkey and avoid getting hit. Another thing I found was that the double death glitch also exists in the game. I died on that same boss while dealing the final blow to Beppi and it registered a Game Over!