So, there are two possibilities here. Either you're too immediately busy right now and can get back to me soon, or you're long-term busy and won't get back to me any time soon and will presumably understand if I press on further without your help.
You haven't been online in a couple of months, so I'm unsure if you'll even read this.

Either way, I had some time tonight, and I did some work on this.
Here's a fixed version of Nippius 2. Now possible to 100% it. I erred slightly more on your side in regards to the ice creams I'd outlined in yellow than I did in our earlier debating I think (the image demonstrating which cones are reasonable/unreasonable is gone, so I'm not certain).

I investigated Dreempipes 2 and discovered that the level's 100% quotas do indeed fail to account for the two unkillable turtles, so here's a fixed version.

I also checked out Deserto 2; it's fine in regards to 100%ability on medium, hard, and turbo. On easy, it's impossible to do it because the enemy that shoots fire doesn't appear on easy, and the 100% completion quotas are shared between easy and medium, so this enemy that only appears on medium and up is required to 100% the level. I'm more comfortable with easy being impossible to 100% complete on this level than I am with medium on this level allowing you to get 100% completion without actually having 100% completion. So, I would err on the side of leaving this one as-is.
As for the enemy-spawning sparkles, they (and their spawn) don't count towards 100% completion (or maybe they do but their spawn don't; I was in a hurry in the last stretch of my testing of the level on hard since I nearly ran out of level time), so aside from 100% speedrunning research, I don't think this matters.

Personally, I'm ready for us to ship the patch. If you don't respond in a few days, I'll assume you don't have time for further input and I'll ask Violet to send what I have so far. Worst case, you respond just after I do this with some complaints or news, and we can ask to do a second patch, which we had discussed doing anyway.