180px-Ghoul Pack

A pack of Ghoul slugs

Ghoul Slugs are dark Slugs created by Dr. Blakk. Ghouls can be created from any Slug. The only known antidote to ghouls are Healer Slugs and the rare Sonikin slug though it (Sonikin)'s healing powers may have been a mistake.'There are 21 different kinds of Ghoul Slugs.'Ghoul Slugs are created by using Dark Water to turn regular Slugs into Ghouls. Ghoul Slugs can only be turned back by healer Slugs. Dr. Blakk uses a small machine that gases a slug and then transforms it. Some slug-shooters prefer these kind of slugs because they are powerful, although ghoul slugs are evil. While ghouls are stronger than regular slugs, it has been seen that a highly trained normal slug can defeat them.  This indicates that ghoul slugs are not automatically stronger than regluar slugs seen in The Trade, where Blakk offers to give Eli his slug back in a stronger state. Overall, the strength of a ghouled slugs is dependent on the overall strength of the slugs original power. A  ghoul can probably get stronger through training like normal slugs. An internet short states ghouls some times run of and form wild packs but this does not seem to line up with the show where a slinger is see calling his scattered ghouls back by a whistling.
180px-Blakk holding a ghoul slug
180px-Dark water