The Vet'ion is a skeletal champion who is located at the "Old Ruins". You can get here by talking to the "Crazy Old Wizard" (Blue Wizard) at home. You need to have 75 Million coins with you in your inventory, not your pouch, or it will not work. Vet'ion has a combat level of 454.
The easiest way to killing Vet'ion is with a "Fast-Hitting" weapon. It's not needed, but, it will make it much easier. You can kill them with anything really. Also, it is recommended that you pray "Soulsplit" (Level 92 prayer required).