Scroll Through Weapons Backwards

I'm not sure if anyone knew you could scroll through your weapons menu backwards, but I found it to be pretty cool. All you have to do is hold A and then tap the Z button, or you hit both at the same time.

Explode Mines Watchless

You can actually blow up remote mines without using the detonator. First, toss the mine as usual but instead of going to the detonator watch, press A and B at the same time. The mine automatically blows up and you still stay on the mine weapons screen.

Pair Up in Multi-Player

Allows more then one person to pick a particular character in multiplayer.

1. Start a four-player match in the multi-player mode, and pick the character you want to "multiply" as Player 4.
2. Pick any other characters for Players 1, 2 and 3.
3. Change the number of Players from 4 to 3, go to the Characters screen again, and select Player 4's character to be Player 3. Pick any characters for Players 1 and 2.
4. Change the number of Players from 3 to 2, go to the Characters screen again, and select Player 4's character to be Player 2. Pick any character for Player 1.
5. Change the number of Players back to 4 and start the game. Players 2, 3 and 4 will be the same character.

Different 2X Weapons

This lets you carry 2 different weapons at the same time. You must have 2 pairs of weapons next to each other in your inventory. And you must do the button presses for the code quickly.
Press and hold the A button.
Before you cycle forward, press Z twice.
Release the A button.
Press A once.
Press Z to fire two or three times to fire while you are changing weapons.
If done correctly, firing the weapon will lock one of the weapons on screen in the middle of changing weapons, leaving you with a mixed pair.