can any 1 tell me how to compltet this task
You can find the recipe for the life-essence on larkinorguide.com. 1 imp's mushroom, 21 essence pebbles (9 vampiric herbs, 3 diamond, 1 wonderflask), 7 soulplaster (5 earthspell, 3 honey balm, 1 egoplasm). And a helpful note: don't make the pebbles or plaster until you have your imp's mushroom, because they get deleted if you complete a king's mission.
Mission 50 takes forethought to complete reliably. If you just go in hoping for a good outcome, you will almost certainly be disappointed. Another advantage of the private forum: no one is going to delete messages containing mission info...! Sandy