Legacy of Santiago
Legacy of Santiago is an ARK expansion that serves as a pre-release test bed for ARK 2's new combat direction. Studio Wildcard has publicly said that new combat systems, including third-person melee and Soulslike-inspired encounters, are being introduced there before they appear in ARK 2.
Why It Exists
Shifting ARK's combat from first-person shooter-with-dinos to third-person, soulslike-influenced melee is a substantial redesign. Legacy of Santiago lets Studio Wildcard test those systems with a live community playing the existing game, gather feedback, and iterate before the sequel ships with the overhauled combat fully baked in.
Feeds ARK 2
Studio Wildcard has publicly said Legacy of Santiago feeds into ARK 2's story and gameplay mechanics. That makes it a narrative bridge as well as a technical rehearsal; what happens in Legacy of Santiago is part of how the sequel's world is set up.