The debuff potions concocted by Sebastian Slughorn posed a significant threat to some of Edinburgh's most renowned Rankers.
They were designed to inflict targeted debuffs on Rankers who had been exposed to the Myriad Potioner's specially crafted concoctions.
Sebastian had prepared these potions in advance. After disposing of Sebastian and commandeering Brewmaster's Bounty's cargo, Eren incinerated the ship to eliminate all traces of his possession of such potent potions.
Now, Eren saw fit to utilize these potions, which spelled trouble for Edinburgh's Rankers.
Unlike Sebastian who had used alchemy dolls to deploy his potions, Eren decided to use his shadow-element powers to achieve greater efficiency in potion deployment and effectiveness.