"The "Venenatis" is located in the wilderness. With a combat level of 464. You can get to this boss when you talk to the; "Crazy old wizard" northwest of ::home. He will teleport you for 65 Million coins to the Venenatis. You must have 65 Million coins in your pouch to teleport there, not in your inventory.
The BEST way to kill this boss is using armour such as; normal Torva, Pernix or Virtus set. Due to this boss being located in the wilderness, you will have to be very careful as if you die, you will lose your items upon death if you are skulled, However if un-skulled you will keep 3 items.
As for a weapon you will need to use an AK-47 or Sword of 1K Truths or any weapon not found in the ::oplist. Also, you will need to have at least a level 95 prayer, so you can pray "Soulsplit" (92) and "Turmoil" (95). Which you can switch to at ::edge on the Ancient Alter.
Since the Venenatis is a boss, it is included in the Soul System, converting all common and uncommon drops into souls. The Venenatis, along with all other NPC's in Dreamscape, drop Key Fragments and Treasure Chests