I agree with Goodbye18000 that the stage is much easier than Mighty No. 5's. There are certainly much less enemies here and the spikes are not really placed in areas that are dangerous. I am glad though that there appeared to be quite a lot of new enemies in this stage compared to No. 5's. Helps with the variety. The enemies that send out spiked bouncing balls are pretty cool because if you affect the terrain, you can change where their attack goes, so you need to be careful there.
I personally do not enjoy underwater section that much, but not because I hate water levels, because if you design them well, then they can turn out to be fantastic levels that use the water mechanic really well with other mechanics, such as Treasure Knight's stage in Shovel Knight in my opinion.
With this stage, it feels as if you are thrown into the water and it is just kinda there. It has two unique enemies that are good for the section, but the terrain here is pretty much just a long straight section with some ladders to climb up on eventually. It just doesn't feel that cohesive to me because if you took out the water, like nothing would change about this section because it feels as if it is just not used at all, besides maybe one jump you could not reach with the extra height.
I guess you also need the underwater section for the falling against spike sequence like Megaman, but I personally wished there was more to this section, like perhaps with No. 2 controlling ice, there could be ice chunks that fall throughout the water or could be climbed on, or at least added hazards to make you have to maneuver carefully around the water. It just feels like wasted potential at the moment, though it is not like it is downright terrible or anything, just mediocre in my eyes.
(I also think that the sound of being underwater is quite loud and drowns out both the music and other sound effects too much, and I believe is should be much more quiet.)
Also Goodbye18000, if you continue to head down the spike section, you'll just end falling into the same area, just more leftwards of the big cliff in which you'll run into a few more enemies.
The ice section of the stage is the much better half. There are ice blocks that you can break, in which sometimes you'll have to do so to reach new areas or attack enemies. They also spring up from the ground sometimes so you need to watch where you are going. Gotta be careful sometimes because if you destroy too many, you might prevent yourself from getting certain items or reaching some platforms. The floor is also somewhat slick, but I never found it too noticeable, but it is possible to slide into a pit of spikes if you are not too careful.
Like with the first section though, there are not too many enemies, and it is also much shorter than it as well. Perhaps to make both sections fit better together, they could add in the ice block mechanics to the underwater section, in which you could use them to progressive further in the water.
This stage also has a mini-boss that is basically two robots playing pong who get faster as you fight them. They are pretty enjoyable to fight, and in their second battle, Mighty No .2 will stand above you and try to attack you as well, which I really like because it makes them feel much more alive when they are trying to stop you from progressing in their stage, plus it is a great way to make the fight more difficult.
The boss fight with Mighty No. 2, Cryosphere, though on the easy side, is a really fun fight. She'll hover around with a water blast and try to freeze it on top of you. When she does that, she creates ice blocks, in which she'll stand on top of them and firing ice that sticks to the floor or ice balls that go across the stage. If you get hit, you'll freeze, and then she'll try to damage you by becoming a large spiked ball and landing on you, though you can escape being frozen. During the next half of the battle, she hover and spray a frozen blast up and down, in which you'll have to time your dash correctly to not be frozen.
She is not too difficult compared to Battalion because when she freezes you, she does little damage, in which you can avoid her big damage attack if you get out of being frozen. Perhaps that is what they were going for, but to perhaps make her tougher, she could also have some attacks that just deal damage instead, such as bouncing around the stage as the spike ball, in which her wall can act as a wall to bounce her back as well.
In the stage, you can also see Mighty No. 1 helping you out. I do believe then that as you save the Numbers that they'll begin to help you through the stages, but it might just be as an extra story feature. I mean Mighty No. 1 was kinda in the background destroying ice and stuff, however, it did not really affect your stage at all. With Cryosphere in Battalion's stage though, she froze some enemies, so perhaps it depends on the stage to the extent that they will help.