Deepwater puff eel

A species found on the Disc near the Counterweight Continent. According to Agatean legend, its bladder and spleen were the most tasty of all morsels, and could only be eaten by those beloved of the Gods. This legend is put to test in Mort...

For, while the bladder and spleen of the deepwater puff eel may indeed be delicious, one who eats it will soon be seeing those gods- it's deadly. Both the Emperor and the Grand Vizier, Nine Turning Mirrors, are aware of this; the Grand Vizier having deliberately brought the bladder and spleen to give to the Emperor at a feast (his normal meal was squishi and boiled seaweed). The Emperor and Vizier both try to get the other to eat it until the Emperor must summon four Heavenly Guards to ensure that his Grand Vizier still has an appetite. In the end, Nine Turning Mirrors does indeed eat the bladder and spleen of the deepwater puff eel, and sure enough encounters Mort (in lieu of Death) seconds later...

It seems similar to bloat, a poison made from the liver of the deep sea blowfish. The actual method of death is quite different, however- the Vizier's ears merely begin to ring, his face turns blue, and then he slumps over and dies.