It's pretty notorious for the "10 Clones in 10 Seconds" thing, which I mentioned earlier provided me my only game overs in the main game of KHII. But that's more of a cheap trick than actual difficulty.
But yeah, I can understand technical limitations being an issue for the 1000 Heartless Battle. Still a shame though.
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"But you have been given freedom. Freedom to be...outside."
"I am lightning...the rain transformed."