I was working on a initial description but time went out, but for the records, you have to search for the magic flowers and pick them with right click, then you have to go to the alchemy station and read the recetary, it's not much descriptive but gives you the idea, mix flowers, then potions, and find the ectoplasm potion and take it to the stone's skull pedestal to win.
Also the bar tells the necromancer proximity but it's not that precise (on purpose) so you better take care and look around, and as you may now, never stop walking...
PD: Thanks for your feedback it's grat to know the flaws so I can fix them :3