Spyder is a "web-crawler", a computer virus taken physical form. It appears a half-octopus, half-spider monster with multiple yellow eyes, eight slimy tentacles, and a fanged mouth.
Spyder is capable of existing both within cyberspace and the physical world by pulling itself through computer monitors, and can move and crawl up walls via its many legs. Its bite causes people to slowly lose their memories, and can result in a person becoming either completely brainless or even transforming into a web crawler themselves. Depending on the ending given, the cure for this can range from taking a hot bath to eating computer chips.