Theres a quest that requires you to complete it with 1 hp. That is the booster retrieving quest. Some people suggest to start the quest with 1 hp but thats impossible as there is a boss at the end. Heres how: Get to the 2nd level and you should see a sand pit trap. Remember that trap. Continue until you reach scorpionmon. Defeat him and make your way back to the trap. Jump into the sand pit and you'll die then revive again with 1 hp. Finally make your way to the portal and get your reward.
Note: This will require two controllers, the game will not let you unplug and plug one controller repeatedly.
As with most games of this type, create two characters, the one you intend to play and one to be used as a "Mule." Put them in seperate saves with seperate names and (even better) seperate species.
One of the two will need some amount of money to start.
Simply start a new two-player game, load both characters and give all of one character's cash (And/or items) to the other and save that character (not the Mule) then move everything from the main character to the mule and save that character without saving your main character.
Now simply end the game and start a new one, loading your main and mule and repeat the process.
(It is much faster than walking back to the Caller Keeper)
This sort of trick can also be handy for giving new characters a big head start.
Note that you cannot duplicate Keychains or Booster Packs
The weapons offered during a Multi-player session are more varied and include weapons not usually available for sale in a single-player session (Such as shot and crush-type weapons)