[Third Person POV],
Ace reasoned that he could wait until there was a chance to strike, such as if Andrew Dawn was able to kill the rat queen and stop killing the other mutant rats, but even after waiting for a while, all that happened was the dragon heart emitting more light as more mutant rats dropped 'dead'.
Ace realised he had to take action right away because if he didn't, there might not be enough mutant rats left to meet his final two job requirements, assuming they all died in the hands of others.
If this happens then he will have to go out in the true world and start hunting monsters which had a certain degree of risk since nothing was without risk in the true world.
Ace was about to enter the hole himself as he had this thought. Suddenly, the den began to shake even more violently than it had previously, but this time the cause was not the altercation between Andrew Dawn and the rat queen but rather the dragon heart.
