as an action, you dash in a straight line (1d6*5) +your dex modifier feet long, during this dash, you are invulnerable and you stop when you collide with a creature or object, once stopped, the creature hit must make a con/ strength save equal to 8+your dex mod, if they fail, they are pushed 5 feet away and take 1d6 bludgeoning damage, if they succeed, nothing happens and you are stopped in front of them. using gravity dash doesn't trigger opportunity attacks.