Let's build on that swamp example. I don't think that would be valid, personally. Swamp is a liquid to some degree. Remember Change into Heaven isn't illusory. You're not fooling someone into seeing something that isn't real. You're actually changing the physical properties of a technique. So if you make Swamp into something that looks like the ground, then it might also feel like the ground. If the ground is liquid, then it isn't the ground. See the issue there? I know that way of wording of it is kinda weird. But I think that kind of usage would fail because it just wouldn't make much sense in the end. Kyoka Suigetsu would be more appropriate to compare to something like 5 Elements Illusion (which we will get to soon) than Change into Heaven. Think of Change into Heaven as being constrained not just by your imagination, but also what is reasonably able to exist.Honestly, I have some trouble imagining that. My answer would probably be along the lines of Kyoka Suigetsu's hypnotic abilities from Bleach. You could alter a technique's 'properties' such that they no longer visually resemble what they were created as. For example, changing a fly into a dragon, or a swamp to resemble the ground that originally occupied the space where it was made. That's the best I can come up with before I just confuse or trip over myself trying to stretch the limits of my imagination just short of the point of lunacy.
Surges can still be used, but Kai can be exceeded so that is accurate. Explain this to me - how does the elemental nature of the illusion matter in relation to surges?Gonna go with the obvious answer here and say that it's the ability to boost Genjutsu beyond the point of being breakable in a single surge, or usage of Kai. I will say though, the additional layer of description you can add to your Genjutsu through this technique can help make it more difficult for a target to reasonably deduce that they're in an illusion, so that's another possible answer to your question.
Imbuing a Genjutsu with an elemental nature means that when a surge is used, it interacts with that surge with respect to elemental strengths and weaknesses. Normally when using a surge, it needs to be one rank stronger than the Genjutsu in question. For example, Chidori Nagashi can break Genjutsu up to B-Rank. If you were to imbue, say, an A-Rank Genjutsu with an Earth nature, Nagashi would be able to break that specific Genjutsu because Lightning is strong against Earth. However, if you imbued a B-Rank Genjutsu with a Wind nature, Nagashi would no longer be able to break it, because the Nagashi is now technically equal in strength to the Genjutsu.Surges can still be used, but Kai can be exceeded so that is accurate. Explain this to me - how does the elemental nature of the illusion matter in relation to surges?