Updated.
Shall we work on the "zombify" ability?
Here's a start...
"Zombify" (Su): As a full-round action, a necromantic sludge can flow into the skin of a slain opponent. The victim gains the zombie template for as long as the necromantic sludge inhabits it. The necromantic sludge may discard the body at any time (another full-round action), at which point it becomes an inanimate corpse again.
While controlling a zombie, all damage directed at the creature is absorbed by the zombie first. Targeted spells may not be directed at the sludge, but can be directed at the zombie. If the zombie sustains enough damage in a single attack to destroy it, any remaining damage is transferred to the sludge. The zombie does not benefit from the sludge's reflective spell resistance.
The necromantic sludge uses its own mental ability scores while controlling the zombie. It may wield weapons with the zombie body, and is considered proficient in all simple weapons.
Necromantic sludge reflects spells as a ring of spell turning, except that it reflects 100% of a spell’s or magical item’s effect.
Let's revisit this...
Here are a few existing creatures with similar mechanics.
Spell Reflection (Ex): Any spell or effect that targets the mirror mephit and does not overcome its SR is reflected directly back at the caster or the user of the item that generated it. This new target is entitled to a saving throw if the effect permits one. Area spells are never reflected unless they are visual effects, such as color spray. In this case, only the portion of the area that surrounds the mirror mephit is reflected; all other creatures in the area are affected normally.
Reflective Spell Resistance (Sp): A nerra has a special type of spell resistance that causes any targeted spell it successfully resists to bounce off and reflect back at the caster. The caster becomes either the spell's target or the point of origin for the spell's effect, as appropriate. In addition, nerras are immune to gaze attacks, and such an effect is reflected back to its origin.
For starters, I'm not fond of the fact that the nerra's is spell-like. I think the mirror mephit's could work, if we leave out the visual effect part.
Alternatively, we could give it a new ability, and simply state that it functions as the spell turning spell, with no limits on spell levels.
Preferences?
Looks good to me. One last thing on zombify: should we specify that a "zombie" reduced to 0 hp is hacked to pieces or something and unsuitable for another use as a "zombie vehicle"?
If we're fine with the names zombify and spell reflection, I say we move on to skills and feats. I'd suggest maxing Spot. For feats, maybe Weapon Focus (slam) and maybe Iron Will?
Looks good to me. One last thing on zombify: should we specify that a "zombie" reduced to 0 hp is hacked to pieces or something and unsuitable for another use as a "zombie vehicle"?
If we're fine with the names zombify and spell reflection, I say we move on to skills and feats. I'd suggest maxing Spot. For feats, maybe Weapon Focus (slam) and maybe Iron Will?