Unknown transposition cypher puzzle

Question

The text is:

ntmilEmondt enae
Leala ed hThtrc 
smve till pg   n
tut ane una olas
hrertwil incma t
ieeenak ioo anTl
es otah foer del
smeormresr  nmhi
m  f ugrpsmci io
 thmmoT tir luay
beoa   a nfsoner
t oris sihhsvlad
sb fengtfned ewr
 irnssortaa htam
ervegs  hntgdn i
 senly  ia eoftn
bito itofshirude
 trsecolucfia ra
 phef fid tyaene
thowuoyffi w  ro
nde sr pnfct ta 
 T f  et e a lir
 fhiout ioilimos
utortru  tn  c t
nce  raero  ls n
osenn  bo  Ee ml
Elt  stigsimtet 

It comes with the following riddle, which is part of the intended form of solving the puzzle.

Where Air meets fire
and land marries sea
head south and east
Therein lies the key

I'm pretty sure it's a transposition cypher, based on letter frequencies, but beyond that, I have no idea.

I know that the end result plaintext is a spell in 5th edition D&D, which means it's (probably) in the format:

[Title]

[Ordinal] level [spell school]

[Description]

The [spell school] is Transmutation, and I know that the spell level is a high one, so the [Ordinal] is probably "Sixth" or higher ("Ninth" being the highest possible). This was learnt from in character knowledge. There's also a well above zero chance that the first word of the [Title] is "Elminster's" or "Elminster".

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Does anyone know any good analytical techniques for solving this sort of transposition cypher, some possible cyphers it could be, or perhaps , way of solving it through the "intended" method using the riddle?

Thanks

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Someone asked a question as an answer, and then deleted it (obviously, using an answer to ask a clarifying question is not the way to go about things). The question was something along the lines of 'is it a spell from the D&D 5e PHB?'

The answer was no, probably not. It's a spell for 5e, but this is the third of three puzzles, and the first two were homebrew spells, so I suspect the third will be too. The previous two's names both started with "Elminster's", which is why I suspected this one might as well.

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I used some in-character knowledge to get a clue. Apparently "fire" refers to heating the scroll, and "air" refers to the blank spaces in the text. When the physical scroll was heated* the following map appeared. The blue dots weren't actually there, I've just added them to make clear where the blank spaces are. For reference, the map is of the Moonshae Isles, in Faerûn (part of the Forgotten Realms D&D campaign setting).

Apologies for for the fact that some information was required that would have been impossible for anyone here to obtain on their own. It never occurred to me that such information would have been part of the puzzle.

* unfortunately, the invisible ink had faded by the time I tried this, so it didn't work. The above image is of a separate copy of the scroll, with the text superimposed over it digitally.

Answer 1

I haven't fully worked it out, but the spell appears to be:

Elminster's Elemental Embodiment, Level Eight, Transmutation

And the solution's technique appears to be related to:

Sliding rows and columns "South" and "East" (wrapping around letters that go off the end).

For example, the following image shows a partially corrected (by trial and error) solution:

In it, I've just:

shifted columns south by 1, 1, 0, 0, 2, 1, 1, 3, 3, 1, 2, 2, 3, 1, 1, 0 cells respectively. You can see fairly clearly the first three or so lines, as well as the last several ("This effect lasts for up to a minute, or until concentration is lost").

I don't have more time to work on this, so I'll just dump some final notes here, for others to pick up from:

1. The errors in my transcription clearly seem to correspond in some way to the positions of the islands. I.e. it gets more "corrupted" towards the centre where there are more islands.
2. However, there's still other issues, such as the missing "e" in "Elemental", and "t" in "Embodiment".
2. You clearly need to shift some rows East before (and/or after/during) shifting columns South. For example if you shift the 4th row East by 1 space first, then shift the columns as shown above, you can also read most of lines 4-7: "The caster and up to three willing allies...".
3. It's possible that some of the shifting requires shifting only partial rows/columns...
4. The amount you shift columns South by, initially seems to correlate with the number of blank spaces that appear on island squares in that given column, but it falls apart further along...