I don't know how this isn't a common issue, but poison is incredibly unbalanced. In the earlier floors its manageable, since its not spammed onto you, but in Magma Core snakes are essentially a death sentence to your run, since they add so much poison to you. The worst part about poison is really the fact that there are next to no solutions to poison other than "kill the enemy fast!!!". Yes, there is that one potion that clears all of the effects you have, but it's a one time use, and if you don't get several of those or a god-like build before Magma Core, you're essentially dead. My solution to this problem would be to add items that defend you against poison. Their luck doesn't matter, they could even all be legendary, but at least that means we'd actually have solutions to poison.
Cleansing rag is too weak. you would either need a whetstone item or a ring to effectively counter poison. Also another good change to poison would be that it damages you at the end of the turn so you dont just take damage that is completely unavoidable. Regenerative Whetstone will also only be viable as long as the poison doesnt just kill you instantly and the same goes for regen