A quivering mass of translucent motile plasm from which emerge groping pseudopodia, it appears to be a typical blob monster. But unlike most blobs, this one is very intelligent, and will act with deliberation and stratagem. Being smart it will retreat if appropriate, plan and scavenge to grow and plot vengeance. It can stealthily ooze through a crack of 1/2 or less width, taking a few minutes to do so. It's not so much a simple monster as an oozing villain.
Career - intelligent blob monster 2
All languages of characters absorbed until their bonus LB is gone are known, and careers at original level -2. It can form sensory parts at will. It can emphasize any one sense at a time, taking about a round to reconfigure, the optimized sense being nearly as good as an animal that specializes in it - smell like a dog with a bit of a cold, see like a slightly nearsighted raptor, hear like a slightly deaf bat, pick one. It can form vocal apparatus at will and sound like an eerily altered version of the person whose memory and vocal shape it is borrowing.
Strike with a pseudopod 1d6 acidic attack. Half of all damage absorbed by armor degrades the armor, roll off fractions (1-3 round down, 4-6 round up). Mighty success does both maximum damage and gives an ongoing +2 to hit that target as it begins to engulf, contact broken on a subsequent miss.
Protection d4-1 (half degrades weapon damage permanently by acidic damage, as above for pseudopod strike, but reducing the values of the weapon that hit it, instead of the armor it hit).
Lifeblood 16 + 1 per 50 pounds of flesh it digests, digests a +1 per round in contact with a dead or helpless target (takes 3-5 rounds after a kill to engulf and digest an adult male human target, bonus lasts for a day, if quiescent bonus degrades much more slowly, up to 20x, giving an opportunity to grow huge if it engulfs a lot of creatures).
Movement - it can ooze along at up to about 4 mph, faster than a walk, much slower than a run, but maintaining that pace will burn through 1 LB per hour.
If resting to slow its metabolism to not burn through absorbed lifeblood, it will take a full round after it is aware of enemies to rouse enough to action, and then act at -2 for a round.
It is vulnerable to fire. Plunging a typical torch into it will do it 1d4 of damage on a successful hit, extinguishing the torch. It is particularly vulnerable to alchemical bases, a few ounces of soda ash or ammonia will do it 1d6. Hunters, magicians, alchemists, and scholars might know this (knowledge test on the career, possible retest if there is time and a library to research it) and alchemists are likely to have enough for 1d3 attacks if they have their typical travelling supplies on them (resource test against alchemy career if necessary to determine randomly). Obviously, it will look out for alchemists and flee from prepared ones or fire bearing mobs.
Acidic damage to armor and weapons can develop slowly, mention the sizzle or blackening at first but only inflict the weakening effect after another round or so if you want it to feel a bit more real.