A Scavenging Crab
"Crawling crabs.. These things are the size of horses"
Scavenging Crab is a type of monster seen in Diablo Immortal. They can be found at the Windswept Shoals of Stormpoint.
These crabs warped by the power of the Worldstone shard can be as big as horses. Smaller crabs can hide inside inside corpses to ambush passers by[1].