In your first post you specified a sentient disease. Which by D&D rules puts it at at least Charisma 1 and wisdom 1. That is what oozes get and they are the stupidest things in D&D basically.
Of course, for the sort of things I am am envisioning, you want something vaguely like Intelligence equal to the smartest creature in at least stage 4 (or whatever I picked the stage of the disease at random) or the cube-root of the number of victims (but this option is capped at 4 times the intelligence of the smartest single creature showing symptoms). You note I actually had it using STRATEGY. Of course, I also said that throwing everything that had been suggested in would make it too powerful to throw up against 8th level characters. Naturally dropping the fire-resistance and keeping the SR low or absent help a lot.