I finally finished my no health upgrade run as Sora on GBA (level 64).
Opened all 12 key to rewards chests, reached every objective in 100 acre wood, and got every sleight.
I didn't use as many sleights as a usually do in re: CoM, and I'd say the difficulty was well balanced.
Now, the final boss was definitely something! I've been stuck on Marluxia phase 1 for months. Getting one-tapped here and there. Until I completely changed my deck:
Around 15 0 and 20 9 attack cards, 5 cure cards, 3-4 elixirs, Vexen for the revive ability just in case, and Maleficent for her damage upgrade.
Every time Marluxia used a sleight, I used a 0 card until he stopped doing any and switched to normal attacks. I then repeatedly used Zantetsuken until he only had 3 cards left in this deck, and finished him off. 'twas a long and tedious process.
Second and last phase was a joke difficulty wise. I could counter every card of his with any of mine, none of his attacks killed me in one strike, and he didn't use any sleight. But, I appreciate the theatrics.
Overall, I love Chain of Memories, and Naminé was dealt a terrible hand in this game, I feel so bad for her.
I'm taking a break in the series, but when I go back, it will be with Riku's story in CoM.