The Sandspear is a large ambush crustacean that lies hidden in canyon sand and hunts on sight, targeting both the player and smaller creatures. Its high bulk lets it knock divers around on contact, and it is an apex of its niche — no other fauna prey on it. A juvenile variant exists.
Its one exploitable weakness is stamina: it tires during extended chases. If you cannot break line of sight, leading it on a long pursuit will eventually let you open distance.
Counterplay: scan the seabed for it before crossing open canyon sand, fight with knives, harpoons or vehicle tools if cornered, and use the stamina drain to escape rather than trying to out-damage a 1,000-HP ambusher.