Maximo vs. Army of Zin Cheats

At first level you when you face your first enemy kill them then go to
the man he will give you a key then you go behind his house break the
loose wall open the chest and that's it.

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.

Easy money:
Select an easy level that you have previously completed and relplay it collecting all the money then save it at the end. You will then be able to buy any of the upgrades from the salesman.

All Levels:
L2, R2, R1, L1, triangle(3), square(2), up, down, up, down

Infinite Coins:
R1, L1, L2, R2, up, down, square(2), up, down

Successfully complete a level with all treasure collected, all chests found, and all innocents saved to unlock an entry in the art gallery. Each level unlocks a new art gallery entry.

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.