Unlockable: Sword Upgrades
There are two of these sword upgrades, which will improve the strength of the attacks of the heroic duo in the levels. The following levels hold a Sword Upgrade:

In the Temple Of Terror, look on the left side of the narrow hallway where the enemies burst through the paper walls for the treasure chest.
In the Sand, Sky, Run, and Gold, look to the right of the area where the plants first attack, locating a set of vines to cut away to reveal the treasure chest.

Unlockable: Unlimited Flaming Cutlass/Blade Barrage Power-Ups
Due to a bug in the programming, it is possible to continually power-up the weapons of the heroes. When the necessary 10 of the Grog Bombs/Throwing Axes are compiled, trigger the beginning of the Power-Up, followed immediately by pressing DOWN to switch to the other character. Now switch back and that player will be powered-up but they will have not spent their stockpile. This means that it is possible to keep powering-up, making many battles far easier than they should be!