Death never used curses. Those who died from curses did indeed come to her, but she would not curse someone with death. Her authority might be vast, but it did not include directly killing any living being.
If Death could kill people whenever she wanted, how could there still be living things in these universes?
Death represented only death, not slaughter, much less curses. Death was merely the consequence of such acts; Death could not actively control them.
Did absolutely fatal curses truly exist in the universe?
In Death's view, they did. For example, in a certain universe, there might be a toxin that was absolutely lethal to a particular species. Once poisoned by it, death was inevitable.
From the mystical side, there were indeed curses capable of killing their targets with one hundred percent certainty. There were many ways to cast such curses. Some might be achieved through spells cast by mages or priests, while others might be attached to objects.
However, such curses had distinctive traits. For instance, most of them were only effective within a Single Universe. Once taken to another universe, even the fundamental energy laws would differ, and the curse would naturally lose its effect.
Yet what Death saw was that around every Spider-Man, everyone who had ever said the words "With great power comes great responsibility" to him had died.
Looking at these deaths individually, there was nothing unusual about them. Death could not possibly examine what every person had said before dying, so when she received them, she had not noticed the issue.
But when their deaths were viewed together, it really did resemble a curse. Say a certain sentence, and you would die. If it truly was a curse, then whoever had cast it had to be an extraordinarily powerful being.
However,