Zoroastrianism
Zoroastrianism, the old faith of Persia and of India's Parsis, teaches a wise Creator opposed by a destructive spirit and calls each soul to good thoughts, good words, and good deeds before judgment at a bridge, but no one has kept that standard, and the Gospel declares one God and one Mediator who gave Himself a ransom for all.
The lesson walks through the topic one card at a time. The full study is the complete written article, with its sources.
Who Zarathustra was, and why the dates of his life are disputed
What Zoroastrians believe about Ahura Mazda, Angra Mainyu, asha, druj, fire, and the Chinvat Bridge, from their own sources
What the evidence does and does not support in the claim that the Bible borrowed from Zoroastrianism
How to share the Gospel with a Zoroastrian friend, and what his family may lose