I keep bashing my head against the first watchief I have to kill. Killing 20 Uruks in 2 minutes doesn't seem too bad but I'm like standing in the middle of their camp and like three guys come after me.
I just did that one actually, the 20 guys was fine because letting out the beast things (I forget what they're called) helps a lot, the rest was a lot of hit and run and cheesing them with arrows, that ground pound move really helps with the crowds too