1st answer: As far I know, the fallen is NOT A RARE. its a quest by wyngale on baaluk. you have 10 rounds to beat him, if not, he will cast a unstopable one hit kill spell (battlefield type). If I remember correctly, after koenigdorf it is activated, but dont go into underwalt or it will dissapear ( talk to Wyngale in the Baaluk's pub to activate it )
2nd answer: It is reported that his game over-spell is stoppable with Cachexia on the 360 version (don't know what comes after that). On the PC version this trick doesn't seem to work, if you believe the wikitalk.