Complex sentence: The Mists were discovered by the Inhuman geneticist Randac approximately 25,000 years ago; he immersed himself in the Mists and gained mental powers comparable to the Eternals.
Split into simpler sentences: The Mists were discovered by the Inhuman geneticist Randac approximately 25,000 years ago. He immersed himself in the Mists and gained mental powers comparable to the Eternals.