If you have the pirate seas adventure pack and are in the ruins, put the hidden treasure on the portal of power and find it in the game. After finding it, speak to somebody and then you can find the hidden treasure at the same place again. You can do this over and over, but you may not talk to someone at the moment the hidden treasure opens or else it won't work.
In the last area of Minefield Mishap you must carefully walk through a maze of mines to reach a golden staff. This entire maze can be skipped. After taking the final teleporter, you see the staff item on your characters right. You must collect this in order to complete the challenge. If you walk directly towards the staff and into the first mine on your characters right, you can push and walk through the gap before the mine replaces itself. You'll get knocked back and receive damage, but the mine wall won't replace the detonated mine before you walk through again. This is even easier with characters with a dash move.