Can spawn when reading a tombstone or in the haunted castle, as well as normally in the Swamp. Slow movement with lots of HP. Drops rotten flesh. Be aware, while the ghouls are not particularly dangerous by themselves in an open field, they can be lethal when encountered in an enclosed space. They can block your exits and ruin your day.
There is also an alternate form of ghoul that spawns in the Haunted Castle and Bram's Castle. This is the Enslaved ghoul, who are generally stronger than normal ghouls but also use the spell vampiric aura, giving them a 5 damage minimum as well as lifesteal.