I hope you're okay with me making this thread, Kim; I figured it might be helpful to keep track of your current ideas. Otherwise you could always merge it with one of the other threads, if possible.
Anyway, I have an idea: a bonus boss in the Tower area.
Sycor again, though this time more harder than the previous battle.
More HP, a new strategy, and... who knows, maybe a reward?
The arena, a hallway filled with death traps and very small platforms.
On the start of the battle, however.. those platforms vanish, save for one.
Reaching Sycor will be harder, though - it would require all bosses, save the "Ending Bosses" for the best ending, to have been defeated.
One of the ways to get closer to Sycor in the boss fight would be using those mini-cores as platforms.
While it may rely on fake difficulty as well, it still would be challenging.
I am, of course, probably as mad as a hatter here; you would need superb timing and high HP, not to mention powerful attacks at their best possible levels. But still, a challenge nonetheless.
If people could handle 3-HP runs of Cave Story, why not have a 3-HP run mode in the mod as well that removes the Life Capsules to prevent taking one by accident?
Also, what about Newerth's history? Historians might find it interesting, as might some other people (such as myself).
Feel free to use the ideas, if you'd like