Ooze slime is a translucent yellow-green substance with the consistency of honey. It is a complex material, capable of regulating virtually any organic chemical reaction, as well as acting like a muscle. When young, oozes are simple scavengers, slowly squirming their way through tunnels and caves, eating whatever they find.
As they grow, they get smarter. Sooner or later, a young ooze's dreamlike sentience will direct their body to preserve, rather than dissolve, useful organs.
Most common are bones. Incorporating the skeletons of animals it has eaten allows an ooze to sustain a discrete shape, with useful features like limbs. Ooze skeletons are always unique, created by mixing and matching bones from many creatures. If an ooze is lucky enough to find a set of plate armor, it will wear it like an exoskeleton.
Oozes are also fond of glands. The powerful stomach of an owlbear might be re-purposed as an acid spray, the venomous sting of a wyvern might be implanted at the end of an "arm", and the flame glands of dragon hatchlings have obvious uses.
Oozes are translucent enough that incorporated organs can be seen from the outside. Those familiar with oozes, and with the interiors of local monsters can guess at the capabilities of a mature ooze.