Burrower mob

This creature will be a small, hostile mob that hides underground, moving from one block to another inside it without actually destroying terrain. when it gets close enough, it will spring out from under the player dealing damage if the player doesn't hit it first. It is only vulnerable when out of the ground, and gives a certain small amount of time before it burrows again, giving a chance for the player to attack it. You can tell that the burrower is inside a block because part of its head will show above the block's surface. This mob could be an exclusive mob to either plains or savanna biomes, or caves.