This mod adds risk-reward gameplay to Morrowind's sneaking. While sneaking behind a creature or NPC, charge an attack to place your mark on an enemy. This mark will drain a portion of the target's health opening them up for a strike. But act fast, the mark doesn't last forever, and their health will return when it expires. OpenMW 0.49+ only.

C:\games\OpenMWMods\Gameplay\SlaysAssassinMarkASneakAttackModforOpenMW

SLAY_Assassins_Mark.omwscripts
SLAY_assassin_mark.omwaddon