Even when Walker looked at the brilliant mantis, he could tell that it was barely able to hold on. It did not have the right amount of poison resistance to be able to handle the brutality of the devil centipedes' venom. Let alone the poisons covering its body from moving around all through the poison jungle dungeon.
This left Walker with a bad feeling in the depths of his stomach. The brilliant mantis had been fine with him and his group passing. Even when they had been prepared to attack, it did not react and just watched.
Besides this, he felt some slight connection. A slight agreement that it would fight with them when he had glanced at it. Call it a feeling in the heat of the movement or call it natural intuition. Whatever it was, they had fought besides one another and defeated an apex predator of the poison jungle dungeon.
Leaving things like this would make everything Walker cared about and valued feel pointless.