Based on a few quick searches, the project has multiple issues:
- Contains music which is missing source files, thus the music is nonlibre
https://github.com/00-Evan/shattered-pixel-dungeon/issues/425
- Missing license notices for the multimedia (so-called "asset") files, thus they are potentially nonlibre
https://github.com/00-Evan/shattered-pixel-dungeon/issues/380
- Missing license notices on some files, thus they are potentially nonlibre
https://github.com/00-Evan/shattered-pixel-dungeon/issues/37

And all this is hidden behind the single license slapped on the package; yet another reminder that package license fields are not to be trusted.

The package is written in and depends on Java -- yuck!

This game is in F-Droid, where it is not noted that the program has non-libre components (Anti-Features).

This game is playable without any music and any sounds. Perhaps if someone could modify PKGBUILD to remove potentially suspicious music, the game makes sense to add to repository. Because this is a pixel game, it does not require FPS and graphics - any GPU will have a good job. Even llvmpipe rendering is not discomfort.

I recommend somebody forwards these issues to F-Droid and perhaps Replicant (I don't know if they officially support F-Droid or use their own repos).

GNUtoo is a member of the Replicant project AFAIK.

In order to package this game, we would either have to:
a. remove the nonlibre and potentially nonlibre files, and seeing as this includes all the multimedia, graphics, music, and some code, all we would be left with is a partially working game engine written in Java, which isn't very desirable considering we already have general-purpose libre game engines such as Godot, or
b. fix the issues upstream.
AFAICT this would require the project which was forked declare which license the multimedia is licensed under, which has to be libre, and to liberate the source forms of the music.
The project will also have to put proper license notices on all source files.

I would recommend option b.

The package is written in and depends on Java -- yuck!

allow me to unpack that - the non-free files can often be
removed as suggested; but there is a bigger problem inherent to
typical java programs

java programs often do not build from source - java developers
tend to add dependencies (usually hundreds of them) which are
downloaded at build-time - parabola policy is to build all
software in a clean chroot, without networking

furthermore, the dependencies are usually binary, but
regardless, they would not be in the source package, which makes
the package non-reproducible, even if parabola packaged it

In order to package this game, we would either have to:
a. .....
b. .....

and c: determine if it requires external dependencies, how many
and which ones, and make new packages for each which are not
packaged in arch (probably most are not), and compile and publish
all of those, which could be hundreds of new packages, only for
the sake of one game

in short, it is due to (c), that the desirability/workload ratio
is usually very low for java programs, regardless of how desirable
or libre they may be