Final answer:
In Zoroastrianism, the 'bad twin' of Ahura Mazda is Angra Mainyu, who represents evil and destruction.
Step-by-step explanation:
In Zoroastrianism, the 'bad twin' of Ahura Mazda is Angra Mainyu. Zoroaster, the founder of Zoroastrianism, emphasized the perpetual conflict between the forces of good and evil. Ahura Mazda represents goodness and wisdom, while Angra Mainyu represents destruction and evil.