Turns out you also can't swim above this spot.
Edit: With the flippers, you can actually dive right through these blocks. Though I'm not sure anything can be done about that.
Edit 2: This text box suddenly popped up when I reached that spot, despite me having already seen the same text when I fell into the Rosecore. Perhaps it's because I also got the text box for the Altar of Xethiz?
Edit 3: The guide should be updated to make it clear that the golden scissors and the dream sphere are locked behind defeating Nyx. It currently claims you just need the lava armor. Though that might be difficult to do, since there's only one cell for the Rosecore before the Astral Corruption happens.
Edit 4: Looking at the guide, it appears that perhaps the evil wizard flag is actually meant to be triggered by saving Gustav's lion in the Valley of Rust. So perhaps it actually is working correctly after all. It's just a bit weird that you can save the lion before even learning that it got kidnapped.
Edit 5: The dialog for the yellow wizard who can remove Nyx's barrier is bugged. He falsely claimed I still needed two more feathers. Perhaps it's because you didn't expect players to have not only the two feathers from the evil wizard tents, but also the one from the Rosecore? Regardless, I was still able to progress.
On a side note, these weird floating enemies in the Forbidding Archives rotate so rapidly that looking at them too closely actually makes me physically uncomfortable due to my photosensitivity. Can the rate at which they rotate be slowed down?
Edit 6: Is the entrance to that house supposed to disappear once the Valley of Rust becomes the Valley of Dust?
Edit 7: It seems Gustav is quite the escape artist. If you reach Nyx, you can see him and his lion locked up. But if you then return to his farm instead of fighting Nyx, both will be there.
Edit 8: I believe it got nerfed, but the third-last phase of the Nyx battle is still by far the hardest for me. I find that I can only really keep track of the projectiles somewhat reliably while I'm holding down the button. I usually died either before or after that. Dodging side shooters from both directions at a medium distance is already hard by itself. With the addition of lots of homing projectiles, it becomes more than I can keep track of at once.
Edit 9: What's that item near the right wall in the Penitence Village shop supposed to be? It looks like the thing marking the last column of the guide. Don't recall what that is, but I don't have it yet. So the shopkeeper's claim that I already have everything he sells except the watch isn't really true. Also, is that magnet supposed to represent anything? Technically, I don't have that either.
Edit 10: The moon has plenty of spots where enemies can partially shoot through solid tiles as long as you don't have the radiation suit. Was that a side effect of implementing the whole radioactivity mechanic?
Also, the first part of climbing up that tower on the moon (don't remember the location's name and wasn't able to take screenshots) is arguably a bit too hard. You already have to make a rather difficult jump there, but then there's also a side shooter. I'd probably either get rid of it or place a save spot just before the jump.
And some of the moon lord trial's phases are pretty hard, but others are remarkably easy. The phase with the spikey balls in particular can be won by doing literally nothing.
Edit 11: Currently dealing with the defense missions close to the end game. So far, they have indeed gotten more challenging. There are still some relatively easy phases, but not many effortless ones anymore. Though I still managed to find a blind spot in the third-last phase of the Azure Output mission and a near-blind spot in the second-last one. I'd have taken screenshots, but that never works while I'm in the middle of gameplay. It seems my controller mapper somehow interferes with it. Both of them were in corners near the left edge of the screen.
Edit 12: The Mount StarFlame defense mission was by far the easiest so far. I still found blind spots in three of the phases. Again, I couldn't take screenshots, but hiding in corners can prove very effective at times.
Edit 13: Peach Woods was also mostly easy. Only found a complete blind spot in one of the first phases, but some others had spots that protected me against all attacks except those from one of these enemies that crawl on the ceiling and shoot fireballs. They're not dangerous by themselves.
Edit 14: Pumpkin Village was harder overall, but still had a few spots that offered guaranteed protection or close to that. The second (?) phase allowed me to hide in the corner on the right edge of the screen. Another one let use the water to block all projectiles (though perhaps you were aware of that, given that a later phase on that screen put lots of slimes in there). And the last one let me hide next to the fan.
Edit 15: Aside from the last phase, Ellictus was incredibly easy. With flames as the only noteworthy hazard, most phases just involved charging towards him.
Edit 16: I had to use the guide to figure out what place Orange Valley is supposed to be. The map still calls it the Abandoned Camp.
Edit 17: Okay, so Agatrix is also one of Xethiz's minions? In that case, why did she throw the fight in the arena? I originally assumed she was just some random weakling who had no idea what she signed up for.
Edit 18: The difficulty of the second phase of Agatrix's true form is heavily dependent on the starting direction of the ghost slime. If it goes left, it's incredibly tough, seeing how it will get in your way before you're quite done pressing the button. If it goes right, it's notably easier, but still the hardest phase.
Edit 19: Do Ellictus and Agatrix really have the same sprite? They do on the guide.
Edit 20: The world map behaved a bit weirdly after Xethiz appeared. At first, my movement was slowed down and I couldn't enter locations. But after moving to the screen to the right, the normal behavior was restored again. Was this deliberate?
Edit 21: The first Eternal Annihilation mission has a phase with a huge amount of slowdown. However, this doesn't affect the real timer, so it runs out long before the visually displayed one.
Edit 22: At the end of Bella's Eternal Annihilation phase, I could see the screen with Gustav for a split second before it turned white and faded back to it. That didn't happen with the others so far.
Edit 23: You forgot to update a damaged house in the credits image for Autumn Village.
Edit 24: The credits image for Penitence Village needs to be updated to no longer say Penitance Village.
Edit 25: Does its credits image really depict the foliage in the Celestial Oasis accurately? I thought it had a trippy filter applied to it.
Edit 26: I think black text would be more readable on the Wyrmridon Catacombs' half of their credits image.
Edit 27: The first credits image for the COs doesn't actually say who made the extra spreadsheet icons.
Edit 28: The last credits image doesn't seem to say who made the sprites for the five disciples.