Generic Forest?: Other than Kamek, I think you should expand the area more, and create a boss fight before the portal to Hyrule, otherwise just make Kamek stronger and move his fight there.
Sigma's Fortress: How about due to the extreme cold outside, all allied heroes suffer like 5 damage per second when outside the fortress, especially might make Velguarder's fight a little more challenging, don't you think?
Also, I think you should probably add a tiny bit more to Sigma's fight, after all, Nightmare Zero even has a better battle than he does. Give him minions at least, or something that hits and bounces around the walls in the boss room.
The Crater: There is not much I can say, but how about two things for this area:
1) At certain points in the area, there are rockslides that fall down from the walls or something, if you catch my gist.
2) At around 5 mins, you can probably add some sort of meteorites that fall down to add realism. Similar to like Sigma's Fortress when escaping, except less frequently.
Halo: Well, Halo is a very hard area to actually think about so I dunno for now.
Hyrule Castle: Well truth be told, if this were an LoZ area all the way, then I would give you lots of ideas, sadly, since its a Haloish area, can't say much to improve it really.
Bowser's Castle Area: Well, pretty much expand Bowser's Castle more and perhaps do something about Wario's boss fight, other than that I got nothing.
Angel Isla ... err I mean ... Green Hill Zone: I think you should make an even more powerful Droid than the Super, something that at least has a chance against Eggman's droids and let them drop the Emeralds after death. Improve on Metal Sonic and the "Dark" Eggman's boss fights. Also be sure to make killing the More powerful than Super Droids mandatory I guess, Idk.
Megaman Zero's stage (Too lazy to check the stage name): You should probably make this area a little more similar to Sigma's Fortress but with a huge twist in some way (Like adding traps), since at around this point, most people get bored and add another boss battle if you can. Improve on Omega Zero's boss fight and so forth.
Ganon's Castle: Apparently, since this is the only mandatory Zelda area other than Hyrule Castle, definitely should make the Castle more enermous. For example, you should make each path to a boss fight a challenge in some way, like locked doors and you have to go through a maze/a path of trap(s) to get a key to unlock them. Also, add some Darknuts, Darknuts are awesome!
Approved
But i'll just say one thing, LINK HAS TOO MANY ITEMS, Cloud actually has too little items imo. Once you make Fenrir and Shadow Flare Materia, generally Cloud only has 2 items in the end. Both of them not very good later on.
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