Here is the Skullduggery Island Guide, written by Nameless UnDEFiNed:

When you land on Skullduggery Island, immediately run to the right. Go inside the General Store, click on the mirror; it’s on the top shelf, right side of the store. The Store Clerk will give you the mirror for free, so now you leave. Run to the right, a little farther, and go right, off of ‘Main Street’. Now, on the right side of the bridge, climb down below the rocks and go left. Get the doubloon, I squared it in the picture (\/)

Now go back to the right, and then back to the General Store, which is to the left of the bridge. Use the Doubloon and buy the feed, then go to the left of the General Store and use the bag to feed the chickens. He can’t afford to pay you back, so he gives you one of his chickens. Now that you have the chicken, go back to the right side of the bridge and release the chicken. The man whose fleas were just eaten by your chicken, gives you a special candle. Go to the top of the hill, on the right (>>), and enter the Governors House. Once you enter the house, use the ‘Special Candle’ and speak with the Governor.

Now that you have your orders, go back to the ‘Main Street’ and climb up the wood area, it looks like this:

Now when you reach the top, there should be a telescope. Look through it, and search all the way to the left (<<) and signal the boat. Now, climb aboard matey, and set sails for Parrot Port, which is to the right (>> almost straight) of Fort Ridley (Your current location). When you land on Parrot Port, talk to the Parrot. Then run back into the water and jump on top of the trading post, you’ll see the parrot.

 

Now, jump across the Straw Roof and jump along over to the Pub, then stand on the vent and run to the right. You’ll see him again on some trees, talk to him again and then go INSIDE the Pub (<<).

 

Go to the second floor and on the left, pick up the cracker on the ground, now leave again. Run to the right, past the trading post, and climb up the tower to talk to the pirate. After you talk to him, jump down and use the cracker. Then go back to the pirate.   You got the map piece! Now you can leave Parrot Port.

Head down on the map, to the Island that looks nearly directly under Parrot Port  . It’s Golden Harbor. **Watch for the rocks, they’ll kinda trash the boat… And before you dock, see if you can pick up floating ‘loot’** When you dock, run to the right, and trade the most expensive things in, and then buy as much of the cheapest item you can.  Walk to the right a little more and you’ll see a small carving, you need to click on the lamps to get the next piece of the map. Here’s the order you need to click on the 5 lamps:

 

Now, you can leave again. Head all the way to the left of the map, and land here:

 

Now, at the trading post, do the exact same thing you did before, sell the most expensive stuff, buy the cheapest. Then, go over to the left and jump up a little bit, and push the ‘Danger Explosives’ barrel down under the giant skull-face rock. Now, go all the way to the top where the Cannonry is, and climb the building. Get the Cannon Starter Kit that’s under the flag. And then go down to the cannon that is straight to the left (<<) of where you put the explosives.

 

Now click on that cannon, and then it should hit the explosives. Where the piece of gold was lodged in the Skull-Face’s mouth, there’s the next map piece. Grab it and go to the next outpost. When you land at Dragon’s Cove, go trade again, and then go down to the bottom right. When you see the old guy on a crate, get on the left side of him (<<) and push him to the right of the bell (just in front of the first barrel is good). Now, run back to where the old guy was, and then jump on the stone dragon’s head. Get the stick on the stone next to you. Jump up to the bell, and use the stick 

 

And you get the next map piece! AWESOME! One more to go! So leave Dragon’s Cove and then head for the next outpost of the semi-circle, Bouffant Bay. When you land on this outpost, go to the right, where the hanging plants are. Jump up and hit the 3rd plant, the 1st plant, and then the 2nd to get the map piece.

 

Now you have all of the map pieces, but you can’t go to Skullduggery yet! You need to get the best ship, and have all of your crew. So, go from post to post trading, but don’t buy on Parrot Port, they’re too expensive. Here are the trading areas, starting with Golden Harbor:

• Golden Harbor ~ Sell
• Pirate Outpost ~ Sell
• Dragon Cove ~ Sell all expensive salvage ~ Buy
• Bouffant Bay ~ Sell silk ~ Buy medicine
• Parrot Port ~ Sell medicine ~ Buy nothing

You could take out a loan to buy a better ship, but I don’t recommend unless you’re getting the last ship: Phoenix Warbird. You buy ships at Ship Shape in Dragon Cove. Here are the boat upgrade prices:

• Jimmy Rigger ~ 3,000 Doubloons ~ Discount – 
• Clarabelle ~ 9,000 Doubloons
• Sea Sultan ~ 30,000 Doubloons
• The Koi ~ 90,000 Doubloons
• Steaming Fury ~ 300,000 Doubloons
• Phoenix Warbird ~ 1,000,000 Doubloons 

**You get a very small discount for trade-ins.**

Here are the Crew Prices:

• Cook (Default)
• Cabin Boy (Default)
• Cargo Master (Found in  Bouffant Bay, gives extra cargo space, EXP. 20 space -> 30 space) 15,000 doubloons
  
• Navigator (Found in Parrot Port, increases Ship Speed) 12,000 doubloons
  
• Cannoneer (Found in Pirate Outpost, loads cannons quicker) 20,000 doubloons
• Shipwright (Found in Dragon Cove, repairs ship without docking.) 20,000 doubloons
  

Time to beat Captain Crawfish, it’s a little tricky, but you just need to know what to do. So, here’s what to do:  Sail around Skullduggery, where most of the pirates hang out, and then when you see Captain Crawfish, fire at him until about a fifth of his ship’s life is gone. Then turn, and crash into him head-on. Both ships will start losing life rapidly. This works, but you should also keep shooting at him non-stop to make sure he loses before you.   Once you have defeated Captain Crawfish, go back to Fort Ridley.

(For this next part, I can’t take pictures right now, my laptop isn’t working right, and there isn’t a screenshot tool on this computer…)

Go all the way to the Governor’s House (In Fort Ridley, where you started), and then back to Skullduggery with your shovel. Now, land on Skullduggery Island, take six steps away from the black flag, and dig. Then Captain Crawfish will appear. Your crew will beat him, he’ll stay, and you’ll get your Medallion!