Source: Bestiary 3, pg(s). 35
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In life, baykoks were hunters who became utterly obsessed with the thrill of chasing and killing. When these hunters die before they can capture and kill their quarry, they sometimes rise from death as baykoks.
A baykok seeks always to prove its mastery of the hunt. It often fixates on the most powerful foe in a group, only picking off lesser foes if they get in the way. After having killed the prey, the baykok swoops down to devour its soul to prevent it from ever returning to seek revenge.