[Third Person POV],
Some of the mutated earth rats eventually became accustomed to the violent shaking and could stand on their feet a little more firmly than before, so they decided to assist the rat fighting Andrew Dawn.
Unlike the other types of earth rats, who could use a little magic, the red skinned rats bartered their ability to cast magic for a stronger physique, allowing them to only fight in close combat.
The other mutated rats, unlike the huge earth rat fighting Andrew Dawn, could not endanger Andrew Dawn's life, but their numbers were more than enough to cause problems for him if they teamed up with the huge rat to fight him. It will make the fight more difficult and reduce his chances of victory.