Formal:
* The soothsayer predicted the king's downfall, but his warnings were ignored.
* Ancient civilizations often consulted soothsayers for guidance on important matters.
Informal:
* My friend claims to be a soothsayer, but I'm not sure I believe her.
* The soothsayer at the carnival told me I would find true love this year, but I'm still single.
Figurative:
* The stock market analyst was known as a soothsayer for his accurate predictions.
* After years of studying the weather patterns, the farmer became a soothsayer of the harvest.
You can also use "soothsayer" in a sentence to describe someone who is good at predicting things, even if they don't use supernatural means:
* My grandma is a bit of a soothsayer when it comes to family drama. She always knows who's going to fight with who next.