The Three God Snake is a very special monster; if one is confident in either being hit once or not being hit at all, then this snake is basically not very harmful or toxic.
But if bitten twice, then the poison is severe, and the health points plummet rapidly; without an Antidote Princess, you're basically left with no choice but to die.
If bitten a third time, then I'm sorry, death is almost certain, and it usually happens instantaneously.
Of course, the Three God Snake is not invincible; it can be defeated.
One simple way is relying on technique and equipment—as fierce as the snake's teeth might be, they are not very long. Plate armor can defend against such attacks, as long as the skin is not bitten, there's basically no threat. Or, by relying on extremely high agility to perfectly dodge.