The final treasure you're seeking is the Lamp of Eternity. It's somewhere inside a large, creepy castle. From the start, head toward the right and you'll find first a disembodied hand carrying a lantern, then a frog jumping around over a series of four circular blocks. If you break away all but the second from the left, you can swipe at it from the left side to send it flying to a treasure chest nearby, which holds a large diamond. When that's collected, go ahead and climb the chain into the next room.

The ledge from which this chain hangs supports a treasure chest with another large diamond. Watch out for the floating hand in the same area. Go ahead and move toward the right, where you'll see a platform sitting at the left side of a rail system. When you jump on it, the platform will start following the track toward the right. Before it drops into the abyss, leap to the second one of these, then ride it over and leap to the safety of a solid stone ledge.
To the right, there's another platform with a chain hanging from it. If you bounce along the wall just to the right (ignoring the chain for a moment), you'll cause a treasure chest to appear. Pogo up to the newly-revealed chest, and bounce from it over the wall leading to your right (be careful to avoid an additional disembodied hand that frequents the area). Here, you'll find a series of blocks over a pit of spikes. Break away the blocks and pogo down to the spikes, then through the wall to the right. Here you can collect diamonds and even a 1-up doll (though watch for the square block in the floor at the center of the room, as it's false; hop over it when you head right to collect the diamond and doll from the treasure chests along the right wall). With that collected, you can return left to the chain and descend it into the next room.

Here, you'll see a gap to the left, with two blocks in the way. You can jump against them and swipe them to remove them, but all you find to the left is some small diamonds and an ice cream cone. It's hardly worth the effort. To the right, however, you will find a 'down' block, as well as a moving suit of armor that would love to damage your life meter. Stand on the hovering 'down' block to reveal a series of hidden ledges. Cross them (watching for another floating hand just to the right) and bounce from the third of them to the fourth with your pogo stick (a regular hop simply won't suffice). From that fourth block, hop right and collect the red diamond and large diamond from the two treasure chests. You'll have to break away two blocks to do so. Next, drop down and walk along the ground toward the right.
You will next see a recess with four blocks hanging over it. Break those, watching for the hand that will be floating toward you from the right. When it's safe, drop down and pull on the handle in the lower right corner of that recess. You'll cause a new block to emerge from the wall above. Jump to it from the ledge just to your left, and then from that block up to the wall to the right. Continue in that direction to find a chain hanging over a bottomless pit. Here, more of the hands will try to knock you into the pit, but you can just cling to the rings and use them to safely reach the chain. Climb it up through the next room, and into the next from there.

Now you should see a large treasure chest to the right. Hop left off the chain (minding the frog) and then pogo over to the ledge to the right. Walk over to the blocks, break them with your pogo stick, and open the treasure chest to reveal a red diamond. Now head toward the left from the chain, to where another rail system works. As you ride it left, watch out for the floating hand. There's also a treasure chest you can pogo to if you're feeling particularly gutsy. However, the hand floating through the area will likely keep you too busy for that. At the end of the second track is a ring suspended in the air above. Be prepared to pogo up to it, then to hop left from there to where Launchpad is waiting just below a chain.
To the left of Launchpad, there are blocks along the ground. Break them away and you'll find you can walk through the lower portion of the wall, to a treasure room. It contains several hidden chests, and you can break them open to collect goodies (large, small, and red diamonds). Then return to your pilot and, if you wish, accept his ride back to Duckburg. Otherwise, go ahead and climb the chain into the next room.

At the top of the chain, head left against the wall for the red and large diamonds those chests contain. There's another floating hand nearby, as you might expect. When you have that treasure, turn to the right and pogo over some spikes while keeping an eye on the spikes protruding from the ceiling. Beyond, you'll see a chain leading up into the next room. If you wish, you can also head to the right for a large diamond hidden against a wall, though at this point you might just prefer to skip that unnecessary step and head up the chain.
In the next room, note that you can walk through the wall to the right to find yourself on a narrow ledge looking over an abyss. A floating hand will approach from the upper right, the first of a wave of three such hands. If you manage to use them as stepping stools, you can cross the pit to the right and find a high ledge with nothing on it. Right from that ledge, you can drop down to the screen below and find a large treasure chest. It contains a
piece of the treasure map.

Note that once you grab this piece, it is likely the last one remaining (provided you purchased the one from the store). The game will now pull you out of the level, back to the store, where you can stock up on items before it will plop you down into a special hidden stage.
Eventually, you'll have to return to this stage to complete it properly. Do so and return to the place where you got the map piece, just as a point of reference. Note that there are four other chests in the same room, and they contain diamonds of varying size. You can head left over the ceiling from there, back to the chain. Climb to the top of that chain and this time head left.

As you advance left, watch for both a flying hand and a piece of animated armor. You'll soon discover another of the rail platforms, kept hidden under a series of blocks. Break those blocks with your pogo stick, touch the platform, then quickly hop to the ledge to the upper left. The platform will ride the rails leading left, and you must cross overhead (the treasure chests along the way contain only a red diamond and a large one) then drop onto the platform as it proceeds left. Continue left (there's another floating hand, but he's not likely to knock you off unless you're jumping at an inopportune moment) and jump to safety. Then push left again to a chain. The treasure chest along the wall to the left contains a large diamond. Collect it, then follow the chain down to the room below.
Here, you can break away the blocks along the wall and pogo along its side to find an ice cream cone, if your life meter isn't full. With that done, head left through the narrow gap to face the stage's boss.
Duck Wizard
Like most bosses up to this late stage in the game, this particular fellow is a bit of a pushover. He really has a pattern you should easily be able to adapt to.
When he first appears, he's likely to do so in two pieces, one to your left and one to your right. From there, he will flicker out of sight. When he reappears, it will be to your left of right, where he will either bring down a bolt of lightning or whip out a tornado. The lightning is easily avoided if you keep moving and aren't near him, while the wind attack scoots along the floor and can be jumped.
To win, you'll need to be in proper position to bounce on his head during the brief moment he has materialized fully. Five strikes with the business end of your pogo stick will send him packing and lead you to the treasure.
NEXT: Under Ground