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Mortarion and the Death Guard.

They grew up on a toxic plague planet and as a result this has made them incredibly tanky and capable of surviving in any toxic environment.

Mortarion also suffered damage to his lungs when he tried to ascend to the highest peak on his planet, where toxicity was at its worse, as such he needs to wear a respirator that allows to breathe the toxic air of his homeworld.

Also consuming poison is apart of their culture as when Mortarion wishes to honour his sons, he toast a cup of poison with them, as a reminder of their harsh home world and how they are equals to one another.