ALT X is an interdimensional entity that invades Sonic's universe and wreaks havoc on the islands and their inhabitants. Its personality is that of a childish entertainer, who has been observing Sonic the Hedgehog since the early days of his time. (Hence why "he" appears to him as Classic Sonic at first, before shifting to a more modern form.) X's goal is to morph and mess with Sonic's world, just to see how much strain he can put on it, but he doesn't kill anyone. The most damage he chooses to do is in the form of amalgamating living creatures and environments, never actually ending a life, but putting them through abstract torment either with changing their bodies or haunting their subconscious with endless nightmares where he puts himself center stage. He would rather savor messing with the Sonic and his friends, however, keeping them as trophies, or constantly playing with them like food. The real problem emerges from the fact he'd want to do this with them FOREVER.