One who predicts or spreads doom and gloom, often pessimistically forecasting negative outcomes.

नाशक

English Usage: The politician was labeled a doom-monger for his constant warnings about the economy.

Hindi Usage: राजनीतिज्ञ को उसकी लगातार आर्थिक चेतावनियों के लिए नाशक के रूप में टैग किया गया।