2- When the player is on a narrow space and ducks, he can't gain any speed:
My guess is that ducking in SMBX 1.4 decelerates the player. But in fact, the physics should not be altered, being duck only makes the game ignore left and right inputs (by that mean, not letting the player moving). It's hard to tell the problem though.
IMAGE BLOCKED,and also need infomation about how it should work in 1.3