Sen'jin Fetish
Sold by Samamba. This is actually three pets in one. You won't know what you'll get until you summon it! Undead type. This pet is a SLOW pet which makes its Dark Simulacrum ability much much less useful.
The Sen'jin Fetish is a Horde companion pet purchased during the Argent Tournament event in Wrath of the Lich King, and when summoned it randomly displays one of three different ghostly mask faces.
Guide awaiting review
Locate Vendor Samamba
Travel to Icecrown and find Samamba at 76, 24.4 to purchase the Sen'jin Fetish.
Purchase Sen'jin Fetish
Buy the Sen'jin Fetish from Samamba for 
40 Champion's Seals. If you don't like the face variant you receive on summoning, simply dismiss and resummon the pet to randomly get one of the three different mask appearances.
Tips
The Sen'jin Fetish is actually three pets in one — each summon randomly displays one of three different mask faces, so dismiss and resummon until you see the one you want.
