The mark is random chance and can take many kills to trigger mark completion. An immortal stated '100 is a reasonable average for that mark' to give a rough reference to how long you may take to get the mark.
A wuggly-ump is drained on the head with your necromancy causing lethal damage. A wuggly-ump has been slain! Traumatized by the shadow and seared by the light, a wuggly-ump's body fails him. For persevering for more than 6 years, the Powers have granted thee a Mark. You have gained the Mark of Hexennial! You gain 7500 archon points! You receive an orb of Vandemaar. An orb of Vandemaar emits a bright flare of white light as it binds with you. You receive an orb of Vandemaar. An orb of Vandemaar emits a bright flare of white light as it binds with you. You receive an orb of Vandemaar. An orb of Vandemaar emits a bright flare of white light as it binds with you. You gain 120 practices! Your blood freezes as you hear a wuggly-ump's death cry. You receive 0 archon points. A wuggly-ump collapses lifeless to the ground. The severed leg of a wuggly-ump falls to the ground. You take an orb of Vandemaar from the corpse of a wuggly-ump.