Death is the Grim Reaper, The Reaper can destroy souls & send them to his world, Death confronted the Eds before they freed the Army, It told them to join him or he'd do it by force & the Eds ended up sneaking away.
Death: Join me, or I have a different way, my Kiss, A Kiss will allow me to gather your souls.
Eddy: A Kiss, o puuh-lease, Sockhead, how about you get rid of this...
Death: Kiss Kiss, Come, Kiss me.
-The Eds' confrontation with Death
On Planet X, after successfully escaping the X ghosts, The Eds are blocked by Death, who wishes them to follow him to his world, threatening to use a Kiss, A Kiss of Disaster that was painless, Eddy makes fun of the threat, but Death glides at him to Kiss him, The Eds get away quickly by throwing Death away.
Death encounters the Eds & glides on Eddy, to prevent Eddy from kissing Death, Edd uses the X ghost repulsor & Death disappears.
To bring those who refuse to give up their souls to Death, Death has a special way of pulling the soul to him, Through a Kiss called Death's Kiss, Death would grab the victim & force his victim's lips to stick to his & the victim would die.