Homebrew
Earth Glide. The rock rat can burrow through nonmagical, unworked earth and stone. While doing so, the rock rat doesn't disturb the material it moves through. False Appearance. While the rock rat remains motionless, it is indistinguishable from a normal rock. Coalesce. When ten rock rats die within 40 ft of one another, their crumbled bodies have a high chance to coalesce and reanimate into a Giant Dirt Rat.
Bite. Melee Attack Roll: +2, reach 5 ft. Hit: 1 Piercing damage.