Complex sentence: The Narayanastra (IAST:, sanskrit: नारायणास्त्र) is the personal missile weapon of Vishnu in his Narayana form, this astra ("weapon" in Sanskrit) lets loose a powerful tirade of millions of deadly missiles simultaneously.
Split into simpler sentences: The Narayanastra (IAST:, sanskrit: नारायणास्त्र) was the personal missile of lord Vishnu in his Narayana form. This astra ("weapon" in Sanskrit) in turn fires a powerful tirade of millions of deadly missiles simultaneously.