[@mcpop9] Who do you think would win in a fight, your berserker or my  beast. I'm not to sure, since it really depends on how strong she get's with her Madness Enchantment, as well as how reckless she gets. Nidhogg, no matter what, is patient in all things except food. Being trapped for a majority of your life, plotting such bloody revenge, will do that for you. He's a psychopath, but he's a smart psychopath and will make sure to do his best to survive any battle he's in, cause the war isn't his number 1 priority. 

I think Nidhogg's disinterest in the grail gives him an edge over other servant's in survivability as it makes it so that he doesn't care if he wins or loses a battle, as long as he survives it. Unless you piss him off, then he'll do his utmost to torture, kill, then eat you.