Death Stroke is a skill located in the Assassination (which can be found in the Nightblade skill tree). Death Stroke is an ultimate. Death Stroke is a base skill, and can be morphed into Incapacitating Strike or Soul Harvest.
Death Stroke deals the following types of damage: Magic Damage. Which means that it gets buffed by the following blue champion point trees: Elemental Expert, Elf Born, Master at Arms, Spell Erosion. Also the following red champion point trees protect against this skill: Elemental Defender, Iron Clad.