The Strider is very tall and a NPC that come's with the More Combine NPC's Pack. Like the Spider Monster, it can be quickly be killed with anything explosive. It act's the same as a normal Strider with all the cow sound's and that kind of stuff so there's not really alot about this NPC. In Gmod 13, the Strider comes with the game version so theres no need for the addon. It will be hard to import it to Gmod 13 anyways if it wasn't even in the game in the first place.