The environment in Hazy City could previously be said to be pretty shoddy, otherwise, a colossal Skeleton behemoth wouldn't end up drowned alive upon sinking into North Lake.
Zheng Yichen had experienced the formidable power of the Essence of Life, yet in such a low-level environment, such a creature still perished.
Death by suffocation was just like those in-game death methods that ignore all resistances to dying.
To him, death methods such as a pierced heart were no longer of any consequence; as for suffocation... it still posed a threat to him. He could go a long time without breathing, but he still needed a bit of oxygen.
He couldn't ignore death by suffocation, but he had a way to evade it. He had already learned Life Archive, which could be used to feign death in such a situation. The moment he made contact with air, he'd be able to revive.
This was his method, whereas the drowned Skeleton behemoth clearly didn't possess such special abilities.