When unable to use a recovery item for the challenge, simply equip Oathkeeper (acquired after you clear Hollow Bastion,). You can recover health with regen every time you pull off a combo on an enemy, and it will decrease the damage you take overall.
Enter Tag mode and let the DS to idle. Even without other DS or a Wii systems nearby, you will rarely meet random artificial avatars. The avatars may provide you with scratch cards. You can also use them to build your avatar sector down to 100 floors and get all available avatar parts from them.
Unlock the following KeyBlades by performing the corresponding tasks:
KEYBLADE - HOW TO UNLOCK Wishing Star - Defeat the Traverse Town Boss Guard Armor. Lady Luck - Defeat the Wonderland Boss Trick Master. Olympia - Defeat Olympus Coliseum Cerberus and Hades. Three Wishes - Defeat the Agrabah Boss Jafar(Genie). Oblivion - Defeat the Hollow Bastion Part 2 Boss Pete and Data Riku. Zero/One - Defeat all forms of the Hollow Bastion Part 2 Boss Sora's Heartless.
Note: This requires a Wii with internet access. Enter the "Avatar" menu and begin Tag mode. On the Wii, go to the Nintendo Channel. Enter the DS Download Service. Select a demo and have the Wii prepare it for download. When the Wii is transmitting the demo, an avatar balloon popup will appear after a few minutes. Select the balloon and use the scratch card. Exit the transmitting demo screen and go back into it. Select another demo on the Wii and repeat the process.
Complete Olympus Coliseum, then go to the save menu. Choose the "Select A World" option, then go to Olympus Coliseum and select "Questploration". Complete the battle system, save the game, then go outside of the Coliseum. There will be tons of enemies to battle. Defeat them all and go back inside, heal, go outside, and repeat the process.
Unlock the following trophies by performing the corresponding tasks. There are 30 in all. Each one provides a chip for the Stat Matrix that boosts HP by 2, Strength by 1, Magic by 1, and Defense by 1. Also, collecting 20 allows you to view the secret movie video:
TROPHY - HOW TO UNLOCK Avatar Collector - Get 50+% of the Avatar Parts from the Avatar Sector. Avatar Sweeper - Complete all 100 floors in the Avatar Sector. Champion Collector - Find 70+% of all items, cheats, chips, weapons, and abilities. Cheater - Use every one of the cheats. Closed Book - Finish the storyline. Converter LV. 100 - Bring one command to Lv. 100. Converter [CR] LV. 100 - Bring one command to Lv. 100 with the [CR] labeling. Critical Acclaim - Complete all worlds on Critical difficulty. Eliminator - Defeat the Eliminator. Fatal Flawless - Complete a world, start to finish, with the HP Cheat set to 0%. Ice Titan - Beat the Ice Titan in Layer 30 of Olympus Coliseum. Justice for All - Defeat all kinds of enemies, even bosses (except the Buggy Roxas of Hollow Bastion's System Sector), at least once. Lord of Loot - Learn 80+% of what enemies' drops are. Proud Achievement - Complete all worlds on Proud or Critical difficulty. Quest Bester - Finish all quests. Rare Prize Roundup - Find all Rare Prize Blox. Sector Sweeper - Find and finish all floors of all System Sectors, even the extra ones. Sultan of Slot - Put one chip of any type in every slot of the Stat Matrix. Technician - Complete all worlds with a Level under 15. Twilight Triumph - Defeat the mystery opponent of Castle Oblivion. W1 Speed Runner - Complete W1 (Destiny Islands) in 5 minutes or less. W2 Speed Runner - Complete W2 (Traverse Town) in 15 minutes or less. W3 Speed Runner - Complete W3 (Wonderland) in 15 minutes or less. W4 Speed Runner - Complete W4 (Olympus Coliseum) in 10 minutes or less. W5 Speed Runner - Complete W5 (Agrabah) in 15 minutes or less. W6 Speed Runner - Complete W6 (Hollow Bastion Part 1) in 15 minutes or less. W7 Speed Runner - Complete W7 (Hollow Bastion Part 2) in 30 minutes or less. W8 Speed Runner - Complete W8 (Castle Oblivion) in 10 minutes or less. Weapon Wizard - Max out the level of each Keyblade.