Poison immunity (monk), not breathing (various races), blasting open the entrances to increase ventilation
I'd argue that even with poison immunity, you'd need to worry about the presumed lack of oxygen.
Tortle Monk - immune to poison, ac17 at first level, and can hold breath over an hour.
Poison immunity wouldn't help, at best it would prevent the panic feeling and hallucinations caused by breathing in CO, but the lack of oxygen would still kill you.
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Poison immunity (monk), not breathing (various races), blasting open the entrances to increase ventilation
I'd argue that even with poison immunity, you'd need to worry about the presumed lack of oxygen.
Tortle Monk - immune to poison, ac17 at first level, and can hold breath over an hour.
Poison immunity wouldn't help, at best it would prevent the panic feeling and hallucinations caused by breathing in CO, but the lack of oxygen would still kill you.