We don't really know his stamina, I just slapped Athletic cause I didn't know what to use. I do recall him fighting like, from the beginning of the night to sunrise, but I'm still not sure. He was supposed to be some monster that cannot get injured and has an immortal body that doesn't require food and shit.
Regardless, is the ice fog visible? If so, then he can definitely just... not go there. Especially when he has keen senses and can see the fog just freezing everything.
He already has a bunch of danmaku, gets stronger by the second, and if he gets attacked by any ice attack he'll just adapt to it, and his lifeforce absorption exists.
As for the immortality vs lifeforce absorption... why exactly would that matter? It's lifeforce absorption, having immortality doesn't really mean much. If he absorbed the lifeforce of someone, they cannot use any of their attacks anymore, and can barely do anything as their organs are ravished as well.