Advance mode:
To get the advance mode simply finish the game once with any character. The advance mode is slightly harder than the normal mode and you'll encounter a few new ennemies.

Unlimited money:
Enter a shop. Move one of your items to the "Sell" block and press R to move it back to your inventory. Next, pick an item in the shop and move it to your inventory, but do not buy it. Finally, press R and the item you never bought will jump to the "Sell" block. You can sell the shopkeeper their own merchandise