The Serpentine Blade artifact can be found in a cave at Barrows of Udûn, in the north-western part of Udûn.
Serpentine Blade, Orcish, Third Age, 2942
A deadly shiv, this serpentine blade has played a role in many betrayals. Uruk power struggles are legendary, weakness is not tolerated, and warriors move up in ranks by murdering their superiors. The Uruks have been roused by their recent successes in Mordor, and as the soldiers' ambition grows, weapons such as these are becoming more and more common.
"Remember me, filth?
What the -
Change of plans, lads. I'm in charge, and we're gonna tear the Black Hand up.
Don't you forget about me!
Ah, yeah, right. My, uh, memory's not that good."