Hello there, I'm not sure what you mean by 'anything that is impossible to replicate'. Did you mean a sensation in real life that is impossible to recreate in dreams? If so, my answer would be nope. As far as I know, your brain is the best simulator. Anything you can sense and perceive in waking life, you can recreate in dreams. They would both feel the same and realistic, the only difference being the absence of physical stimuli.