There are normal moves that do damage all instantly then there is DoT(Damage Over Time) which does the same damage a normal special move would but over the course of several seconds typically around 10%.
There are different types of DOT:
Proximity DOT is the kind that has an area of effect that inflicts damage to you when you are in that area.
Marked DOT is like a poison. Once you get marked you can't escape the damage its guaranteed.
Marked is the kind that won't kill you because they are stacked on top of full combo like Barakas 40-50% combos plus Mark DOT(+10%).
Proximity is the kind that does kill. This is probably because this type is not guaranteed since you have ways to escape it like: jumping out, Fatal Blow removes it, KB removes it.