Each time people entered the Domain of the Fallen, the Monsters inside it would sense a faint ripple in the air.
This told them that the Humans had once again returned, and it was time to take a bite out of some of them once more.
All the monsters inside the Domain of the Fallen had their own agendas, and they were not allied with each other. All of them were hunters and preyed on each other, which meant that they mustn't engage in a drawn out battle and injure themselves, or else, their rivals would prey upon them.
Everytime the teenagers entered, the Monsters would hide in different places along the route they normally took to ambush them.
Also, they made sure to stay a fair distance from each other, preventing the other monsters from taking advantage of them.