I'm going to explain my thoughts on each part.
MysticSword -
It looks a little..blank. The background effect is pretty good. Not the best but okay. The block designs could be a little better if you added different blocks. But you're making a remake of a level that is on "Geometry Dash Meltdown" so I kind of know why you used those blocks. The gameplay looks pretty fun. You're part doesn't have good sync. Also the ring spinning things you put at the bottom such as at 0:26 or 21% look very out of place. At 22% if you added moving objects there then it could've been good.
Foxy -
I can barely read the text and I was about to count is as your part because they look exactly the same. The gameplay looks a little fun and it isn't synced at all. The custom background is beginning to be a little repetitive because it is still there :v I love how at 38% the text flew in like it does on a Gameboy Advance SP ;3;
GmdEGGZero -
Ok, sooo the background is still there just that it changed to the color of his part. The boss looks pretty good. Just that it looks a bit out of place. I also just saw the face in the background which would look better with out it. And there is nothing exciting about the blocks. The gameplay there looks very boring to. Also this doesn't look like it came from "Geometry Dash Meltdown" Only the blocks do and the face. The sync is really good though. I like how the attack syncs with it.
wantedfrog -
I couldn't tell if his part started because they all look the same. I like what he did with some of the blocks. It doesn't sync at all though. The design is pretty blank. AND I STILL CAN'T BELIEVE THE BACKGROUND IS STILL THERE. I kind of like how you presented your name at 69% but it would look better without the glowing things you put around it.
Noward543 -
I STILL CAN'T BELIEVE THAT SAME BACKGROUND IS STILL THERE... anyways your part is SUPPERRRR blank. I like how you presented your name though. The block design could be better. 83% is a really bad dual part. First off it looks kind of annoying. Second the line you put to seperate it looks ugly there. And wasn't this supposed to be a Meltdown level?! Then why is there blocks used that were used in Blast Processing. The ball part looks kind of boring. If you minimize and turn it back to normal rapidly than I guess it would look kind of fun. At 87% I like how when the platform moves it syncs to the song. I also like how the line tells us were the platform will stop. 89% I like how the slopes sync with the song to.
Kaito -
Your part is probably the best in this level. The custom background changed & It sticked to the Meltdown theme! I love the custom background of the skull! Although it doesn't sync ,it does like pretty fun to play!
Overall this level should have many improvements such as the parts looking at least a little different from each other. And for there to be more design and sync. Overall I give the level a 4/10