Step 1
Talk to the Odd Old Man.
Learn what he needs and learn how to prepare the remains

To begin with, head north-east of Varrock and take the pathway leading north, into a quarry. Once here, speak to the Odd Old Man and he will tell you that he needs skin, hide or fur to continue with a Varrock Museum exhibit. If you continue talking with him, and agree to help him, he will instruct you on what he needs and how to prepare them for him.

You will be required to get: Unicorn hide, Bear pelt, Cave crawler skin, Black Unicorn hide, Cockatrice skin, Hobgoblin skin, Fox pelt, Fenris wolf pelt, and Rock crab carcass.

Step 2
Head to Fremennik province
Kill required monsters

Items needed: Mirror shield

To obtain the Cave crawler skin (beware these might poison you) and Cockatrice skin, you must enter the Fremennik Slayer Dungeon.

To obtain the others, they are located around the Fremennik province.

Black Unicorn hide - Red dot
Bear pelt - Black dot
Fox pelt - Light green dot
Fenris wolf pelt - Purple dot
Rock crab carcass - Dark blue dot
Hobgoblin skin - Light Blue dot
Unicorn hide - Yellow dot

Step 3
Return to the Odd Old Man
Prepare items

Items needed: 9 Bags of salt, 8 Logs (any kind), Tinderbox

Head to the bank in east Varrock. Withdraw all your skins, hides and fur, 9 rock salts, 8 logs and a tinderbox. Head back to the Odd Old Man's hut.

Once back at the Odd Old Man, use a rock salt on each skin, hide and fur. Now place a log in the fire pit, and then place a skin, hide or fur on the stretching rack. Now light the fire pit. Once the fire is gone, remove the skin, hide or fur and repeat this process till all the remaining skin, hide and fur are done.

Talk with the Odd Old Man and he will take the finished products.

Step 4
Read the new Wishlist.
Collect the specified items

After you complete the first part of the quest there is a new wish list posted on the wall of the Odd Old Man's hut. This list has 13 new objects on it. These are shown below.

1. Foot bone of a large ape-like creature - Temple guardian monkey, Cave Horror or a Jungle Horror
2. Sabre-like teeth - Sabre toothed kyatt, Nail beast
3. Long, sharp claws - Nail beast, Gorak or the Giant Mole
4. Fibula bone of the third leg of an adult three-legged creature - Level 87 or 89 Turoth.
5. Very large Hand bone - Large Crawling hand.
6. 9 dragon tail-bones - Green dragon, Blue dragon, Red dragon, Black dragon, Skeletal wyvern, Bronze dragon, Iron dragon, Steel dragon, and Mithril dragon
7. Neck bone of camel - Ugthanki camel.
8. Shoulder of giant - Moss giant, Fire giant, Hill giant, Ice giant, Cyclops
9. Spine of a giant snake - Crash island snake, Sea snake young, Giant Snake
10. Pelvis of a four-legged, magic-casting creature - Aquanite
11. Femur of a large follower of bandos - Bork or General Graardor.
12. Humerus of a large tortoise - Tortoise or a Warped tortoise.
13. Golden fleece - Pay 1k to the troll east of Rellekka.

Step 5
Return to the Odd Old Man's hut.
Prepare the Bones
Prepare for the fight.

Items needed: 20 Logs (any kind), 20 Jugs of Vinegar, 20 Pots, Tinderbox

Head to the bank in east Varrock. If you have 21 pots, fill them up at the bank (add the vinegar to the pot, then add the bones). Deposit all but 13 pots of bones, and withdraw 13 logs and a tinderbox. Now head back to the Odd Old Man's hut.

Once back at the Odd Old Man, put a log in the pot-boiler in front of his hut. Now use a pot containing the bone and vinegar on the pot-boiler, and light it using your tinderbox. After a moment, you can remove the pot from the boiler: you will have a cleaned bone, and an empty pot. Repeat this process for the remaining twelve pots of bones, then head back to Varrock to withdraw the last of your pots of bones and logs. Head back to the Odd Old Man and repeat this step.
Note: If you only have one pot that you're reusing, you will need to take many more trips.

Once you have completed the wishlist, you will need to prepare to fight a level 320 Skeletal horror. Head to varrock bank and prepare your inventory.

Step 6
Defeat Skeletal horror.
Talk to Odd Old Man.

Once you are ready to fight, climb over the bone stiles. The Skeletal horror is level 320 at the beginning, and uses melee and magic to attack you. Pray Protect from Magic and wear defensive armour.

After doing some damage, the Skeletal horror will lose a hand. Quickly grab it and bury it or the Skeletal horror will regain health. After some more health is gone, the Skeletal horror will lose another hand. Quickly grab it and bury.After doing some more damage, the Skeletal horror will lose its tail. Quickly grab it and bury it.

Note: As you bury the fallen limb the Skeletal horror will go down in combat level. If you fail to bury the limb, the Skeletal horror will regain health.

Once you climb over the bone stile and talk with the Odd Old Man he will thank you for rescuing him. Your Ram Skull helmet or Bonesack will be enchanted. These will be able to teleport you back to the Odd Old man so you can fight the Skeletal horror weekly. You will also receive 10,000 Slayer XP and 7,000 Prayer XP the first time you kill it, and every week after that it is 1,250 Slayer XP and 1,000 Prayer XP.