Spend That Loot! Achievement

This achievement is earned by having 65,000 treasure on one Skylander at the one time. It does not count any money already spent. This will not likely happen during your normal playthrough, and will require additional runs. Fortunately, there is a wonderful way to get potentially infinite money once you beat the game.

After the credits end, you are returned to the deck of the Dread-Yacht. Go into the door up the stairs to the right, and make your way up to the Crane Deck. You'll see a very large pile of treasure, around 6000, on the ground. Collect it, and then quit to the dashboard. Do not save and quit the game. The money is saved to your Skylander instantly.

Back at the dashboard, create a copy of your save data on a USB stick. Load up the game using the USB save, and you'll be back on the ship deck. Go back up to the Crane Deck, and you'll see the money is there again. Collect it, dashboard, and reload from the USB. Repeat this until you amass 65,000 treasure and unlock the achievement.

A word of caution: Before attempting this, try to collect all of the Winged Sapphires that can appear randomly around the ship. One can spawn on the Crane Deck, and if you grab it while getting the treasure, the game will save, and you'll lose your infinite money cheat.

Here is a video by Toxiicxducky831 showing the process: