Differences between Easy/Normal/Hard

[Alahra]

From what I can tell, having done both Easy and Normal, the difference is the Ranks of the naturally spawning monsters.

Easy: Rank 1, 2 and 3 monsters spawn naturally.
Normal: Rank 2, 3 and 4 monsters spawn naturally.
Hard(Guess): Rank 3, 4 and 5 monsters spawn naturally.

Rank V monsters can spawn naturally in Normal as well. My last run, we actually have 3 Rank Vs on our starting island, which was pretty weird.