500

There is a situation where a Mewtwo initiates down smash against a Marth. Since Mewtwo's down smash is slow, Marth thinks he has enough time to throw out a Jab to protect himself and start his own combo. Assume that if the Marth were to use the jab, the hit box would become active just as the down smashes hit box becomes active. Should the Marth player go for jab?

No, Since the down smash does 15% and Marth's jab only does a maximum of 5%, the down smash would straight up beat out the jab hit box, as it does over 9% more damage than jab. 8% disparities in ground moves allow them to clank. With 9% disparities, the stronger move beats the weaker move, resembling "priority". Marth would get hit if he went for jab in this situation.