Cleon
Legend
Before moving on, we still need to tackle its odd ability to negate magical weapon bonuses.
Maybe something like a personal-range antimagic field? Particularly this bit: "Furthermore, while a magic sword does not function magically within the area, it is still a sword (and a masterwork sword at that)."
Well obviously it can't be a full antimagic field, since that would make it immune to all sorts of magic, including spells.
How about this:
Quell Enhancement (Su) - A necromantic sludge ignores any enhancement bonus of weapons used against it. Thus, a +3 longsword is effectively just a masterwork longsword when attacking the creature. This protection extends to corpses the sludge is animating with its Zombify power.