I recently beat the Japanese versions of Actraiser and Actraiser 2. I chose the Japanese version for the first game because I read on the internet it's more challenging (plus the usual story of uncensored sprites and "adult" themes and so on). There's some good information about the differences here
, namely that in the Japanese version, spikes kill instantly, magic spells cost variable amounts of MP and not just 1MP like in the overseas versions, more enemies, and so on. However, the sim parts are actually a little harder in the overseas versions (for example, the cherub's health doesn't regenerate as quickly), but the sim parts are so easy that it doesn't really matter.
However, I couldn't find much information about the differences between the various versions of Actraiser 2, so I went with the Japanese version. Only afterwards with deeper research did I find that the American version was made harder. I did some testing between the two versions by playing the Tortoise Island level on all the difficulties, and here's what I found (plus some other information I gleaned from the internet):
In both versions (in my testing, the HP and damage appeared to be the same in the Japanese and American versions):
Easy: lower enemy HP, lower enemy attack damage
Normal: normal enemy HP, normal enemy attack damage
Hard: higher enemy HP, higher enemy attack damage
Easy: 5 lives, 5MP; game ends after the first boss rush against the level mini-bosses, where you are told, "Congratulation! Challenge Normal game!"
Normal: 3 lives, 3MP; game ends after fight with Satan
Hard: 2 lives, 3MP; game ends after fight with Satan, but ending animation is slightly better (ends with a pretty picture instead of a black background)
Easy: 7 lives, 3MP
Normal: 5 lives, 3MP; game ends after fight with Satan, with "good" ending animation; I don't know if this is true for Easy and Hard as well
Hard: 3 lives, 3MP, plus I noticed one of the power-up containers found halfway through the level was removed (I didn't see this in any other scenario)
I barely used magic and beat the Japanese version on normal with a decent amount of challenge, but I think the challenge on Normal in the American version would be more interesting. I found the enemies take far too long to kill in the Hard difficulties, which is more annoying than challenging. If anyone knows of any other differences, please let me know.