One day An Incident occurred in which The Universe would Replace Sonic with an Unknown entity who assumed itself to be Sonic. Being Perfectly Accurate to Sonic's Personality and Abilities and even having His Past Memories, but for whatever reason Its appearance would come out quite different to that of the Blue Blur Himself. and While Nobody Would notice, Tails would, and Tails would begin to realize that his best friend was replaced with an Imposter, and though he'd try to get everyone to notice, Nobody would, and This Enraged tails. and "Sonic" Himself would notice Tails' Bizarre behavior, but, not knowing He ISN'T Sonic, would be Confused with this behavior, trying everything he could to get His Best friend to trust Him again- to No Avail, and while their Adventures would and will continue as normal, Tails KNOWS the truth, and one day, Will Convince everyone of it, but as time goes on, His Obsession with exposing "Sonic"'s True identity will become more and More Deranged, with the truth kept shut, Tails' Madness continue to take over Him

https://continued-exe.fandom.com/wiki/Capgras