Unlimited money and weapons and duplicate characters:
First have a high level character and go to the screen where you pick your character. You must have 2 memory cards for this trick. First have a blank memory card in the first slot and the one with the character you want to duplicate. Go to temp characters and transfer the character. Then switch the memory cards. Pick the character that's being transferred an it will ask you something and reply yes. Then your characters will be on both cards. The only problem is that you will not be able to transfer it back to the original card, but you will have two of them.
Sent in by WvyDvy1

Avoid walking near traps and enemies:-  Normally, you cannot run when near a trap or enemy. To avoid this, press Start to display the main menu. You may now run again.

Kireek's Soul Eater:-  You can do this only once per difficulty setting. To get Kireeks' Soul Eater, you need to play "Dr. Osto's Research" quest. Then, after you get the information at the end, talk to Sue. If she asks your name, say "No". After you finish that quest, go to the "Unsealed Door" quest. You will meet Sue again. Talk to her and listen to what she says. Then, complete the quest. Next, go to the Waterfall Tears. After defeating Anna, continue on to Cave 2 (same quest) and you will eventually meet Kireek. He will greet you, then you will have to fight him. After you defeat him, go to the "Black Paper" quest where he will try a rematch in Cave 1 of this quest. Note: You are in the dark in this battle. When you defeat Kireek in that battle, you will meet him again in the "From the Depths" quest. In that quest after you separate from Ash, go back to Ruins 2 (in this quest) and go as far west you can. You will confront Kireek for the final time. It is recommended that you equip some armor, shields, units that can withstand Dark/Draw/Shadow or whatever that weapon is made out of, or use Razonde (or Zonde, if that is all you have). When you defeat him you get to keep his weapon for your accomplishment.

Dressing Room  -  To unlock the Dressing Room, complete all areas and quests under the normal difficulty setting.

Very hard difficulty setting  -  Successfully complete either episode under the hard difficulty setting to unlock the very hard difficulty setting for both episodes. Note: Get to level 40 or higher to unlock the very hard difficulty setting in online mode.

Ultimate difficulty setting  -  Successfully complete either episode under the very hard difficulty setting to unlock the ultimate difficulty setting for both episodes.
Note: Get to level 80 or higher to unlock the ultimate difficulty setting in online mode.

Get items x99  -  If you do the following steps written below you can get Monomates, Dimates, Trimates, Monofluids, Difluids, Trifluids a.s.o. x99... Here are the required steps:

1. Put 99 Photon Drops in the bank...
2. Put 1 of the item you want to dupe in the bank, and toss the remaining 9 on the ground...
3. Go back to the bank and highlight Photon Drops, choose 99 and answer "No". It's very important to say "No" if the code shall work...
4. Take the item you want to dupe from the bank, the item should still be in the bank after you take it...
5. Look in your inventory, now you got the item x99... Congratulations!

This code even works on Photon Drops and Photon Spheres... Cool huh?!

Ice break:  When you are frozen by an enemy, trap, or Boss, move the Analog-stick Up and Down, or Left to Right very rapidly to break free of the ice. This works very well when fighting Bosses with Ice Element attacks such as the Gol Dragon or Sil Dragon. This trick also works in battle mode.

Very hard difficulty setting:  Successfully complete either episode under the hard difficulty setting to unlock the very hard difficulty setting for both episodes. Note: Get to level 40 or higher to unlock the very hard difficulty setting in online mode.

Chair in Lobby:  Hold X and press A while standing in the lobby to create a chair that matches your character. Press A to move forwards or use the Analog-stick to turn. Press B to get rid of the chair.

Cheap kills:  If you are having trouble in a room, try running out of it and go back in. Some monsters will probably go into a dormant mode and allow you to get off a hit or two before they retaliate. This is especially useful against Garanz.

Refill health:  If you are a robot in the game, you can refill your health after receiving damage from an enemy. Find a safe place to rest and remain in that spot for a least a minute. Your health meter will go up a little bit at a time.

FMV sequences:  To view two FMV sequences (one when you create a character and one new sequence), remain idle at the "Press Start" screen. After the background pulses four times, one of the FMV sequences will start.

Control loading screen:  While going online, move the Analog-stick or C-stick to move the light around the screen. When entering an area, move the Analog-stick to turn the tunnel or the C-stick to change the tunnel's speed.

Tiny Chaos Garden Download to GBA  -  Ok, first HAVE THE GBA LINKED UP ONTO THE 4TH CONTROLLER SLOT! Now, start the quest "The Fake in Yellow"and complete it. Go talk to the proffesor's assistant and he will tell you to get your Meseta. DON'T!!!!!! Go back to the Telepipe and you'll see three Rag Rappies saying something like "P P Pip Piii". Freaky, huh? Now go in the direction they face and stand in the little grass patch with boxes by the stream. A little blue Chaos from Sonic Adventure 2 Battle for the GCN will pop out beside the waterfall in the background. He'll give you a key for the little thing that looks like a tall sideless and topless telephone booth with a GBA sign on it. Return to the city and look for it to the right of the Hunter's Guild. The voice will tell you how to do the rest.Oh, i think it does something on SA2B if you link it up with that game. Have fun! (whew my arms ache now)

REAL Way to Get Dressing Room  -  Get 10,000 Meseta ON YOUR PERSON (not in bank). Quit and go to select a character. When you choose your person with the money, you'll se a fourth option. That's Dressing Room. No need to complete anything (but if you just started out i suggest putting the money on another character and select Recreate).

Weapons from monsters - If you obtain a special item such as G-Assassins Arms or Bomma's Right Arm, go to the Unsealed Door mission. Talk to the person standing to the right of the portal to the principal after all missions are complete. He will turn your item into a weapon.