Quietly and uneventfully, a foreign creature slipped through a crack in their own dimension. The disturbance was so minor that it would be unnoticed by all, yielding only a single creature who crossed over without a bang nor a roar. The entity possessed no form to be seen; an invisible presence similar to that of a spirit. Yet it was not dead. It's life had only just begun. The consciousness had only just been brought into existence, and brought nothing remarkable into the dimension. Another entity who had been freshly split from his mother only a few seconds after coming into existence might have panicked, but the creature possessed zero emotions. All that guided the creature was the instinct to use others for the purposes of it's own survival. It was devoid of emotions and thoughts that might be stirred up by one's feelings. It wandered around following it's instincts, although it did not remain hidden within the shadows forever. The abomination encountered an object of interest.
A sparrow was perched upon the ground in front of it, pecking at the grass. It didn't approach the animal, instead observing it's motions in total silence. Grasping it's bone structure, it acted accordingly. A physical form finally began to form where it stood; bones connecting to form a network of limbs that were then coated with layers upon layers of muscles. The avian it needed in order to copy minute details startled, spreading it's wings and flying in the direction of the treetops in order to escape the mimic. Yet with a memory that was incapable of overlooking even a single feature, it no longer required the avian to be present in order to replicate it's appearance. Flesh covered muscle, and feathers covered flesh. The previously invisible being spread it's own wings and also flew up, replicating every motion it had recorded without difficulty. However, unable to process that the avian had landed, it continued upwards mindlessly in it's experimental fashion. Only when it saw another bird startle and fly straight from one tree to another did it cease to gain altitude and flew straight ahead; halting within the branches of an extremely tall tree just as it had now seen several other creatures with similar appearances do.
The avian looked around from it's perch. By it's logic, it would be capable of spreading it's wings and taking itself down if going up and flying at a constant height were within it's limits. Despite being newly born, it already possessed impressive intelligence for a being who wasn't even a year of age yet. It's potential for learning was infinite, with a brain that could process even the most complex features and adapt them to it's own physiology. After a few minutes of observance, it finally caught sight of a bird landing upon the forest floor. It copied the motion and made an identical landing, experimentally pecking the grass as they had observed the first lifeform doing. It reaped nothing from the task, so it raised it's head and waited for something else to occur that it could experience itself. Educating itself was it's one and only instinct.