Yuni is one of the most mysterious characters. His history and motivations are rather obscure, yet he plays a central role in propagating the loop.
True to his archetype, Yuni is a trickster. But he doesn’t just try to trick the members of the cabin, he also tricks Satoru by withholding information. Yuni knew Enomoto would die, and that Satoru would fall from the clock tower. However, neither Satoru nor Enomoto seem to be aware that these two things will happen.
So what else is Yuni withholding? Does Satoru even know about Hotori lying in the snow and the existence of swaps between Inubushi, Hotori and the female fetus? In any case, Yuni definitely does.
Yuni could have saved Hotori by bringing her body into the cabin, and he could have saved Enomoto by warning him before 2012. Since he did not, he is personally responsible for the deaths of both these people. Perhaps he left Hotori outside so he could preserve food supplies for Kokoro, and let Enomoto’s personality/Satoru’s body die as revenge against Leiblich.