In Horizon Forbidden West, Aloy will encounter new monster types. The first new monster type will be the Burrower, which will appear in the Reach for the Stars main quest. The Reach for the Stars main quest still happen in the Horizon Zero Dawn area. After the Reach for the Stars quest will be the Point of the Lance quest. Then, the hero will get back to Meridian Alight area, and from there get to the Forbidden West lands, where there will be more new machines types and more resources.
The most common resources is the metal shards. After defeating the Burrowers, the hero get metal shards from the Burrowers.