There's a weapon discussed in Mahabharata called Brahmastra. Maybe Bhishma and Drona had this weapon.
How powerful was it? If any person used it, would it destroy whole world? Was there any technique/way to respond to it and make it fail once it is released by someone? Or once released, it will destroy the world?
EDIT: Now since it seems a duplicate, let me add more details to clarify why I need answer for it.
In a few answers earlier on different questions, I read that "Arjuna or someone fired Brahmastra on Karna. The story after being fired is not described. Nobody knows what happened." Then the author concluded that since Karna was still alive, it must have been destroyed with ordinary arrows.
Unfortunately, I can't find those questions and answers, but I'm sure I read it.
EDIT 2: If you still not ready to remove it as duplicate, let me add further details. In Star Plus Mahabharata, it is shown that Brahmastra fired by Ashwathama attacks only the womb of Uttara. No point of destroying whole world. Secondly, it is also shown that Brahmastra fired by Arjuna to counter attack Ashwathama's Brahmastra, withdrawn back by Arjuna after Krishna told him to do so.