Unlockable: Rewards 
If you would like to Master every stage, you will have to do the following: save all 
of the lives of the Innocents, find every one of the buried Treasure Chests (Secret 
Chests), collect every item in the stage (Koins, Diamonds, Armor... Everything, 
basically), and defeat every enemy in the stage (including those Evil Bunnies.) If 
an enemy falls off of the stage, it is counted as a kill. If you collect an item and 
die, you will have still collected the item. You will be rewarded with Art Galleries of 
concept images. 
 
Infinite Goodies 
On Level 9, Down with the Ship, you have three minutes to destroy six reactors. 
Using the Drill Attack, you can destroy a reactor with three hits. Destroy five 
reactors, then spend the rest of your time fighting enemies. You can earn lots of 
money destroying enemies. When time is almost up, destroy the final reactor. Go 
back to Level 2. Purchase power-ups and continues from the merchant then save 
and quit the game. Load your save, return to Level 9 and repeat the tactic. You 
can do this as many times as you like and earn oodles of cash in the process. 

Easy money:
You can replay any level that you have previously completed as many times as 
desired. To get as much money as needed, replay an easy level, collect all the 
money, and save the game at the end. You will now be able to buy any of the 
upgrades that you need from the salesmen.

Monty Python reference:
Sometimes when you see a breakable tree stump there will be a little rabbit 
nearby. If you hit it, it latches on to Maximo in a way that is reminiscent of 
the "Killer bunny" scene from Monty Python And The Holy Grail.