I installed crimsonland (from humble, not gog) and it seems to be missing a dep I never heard of and after trying suggestions from around the web it seems that it is already there somewhere, the game just can't find it

ldd ./crimsonland
linux-gate.so.1 => (0xf77fa000)
libGL.so.1 => /usr/lib32/nvidia-381/libGL.so.1 (0xf7742000)
libSDL2-2.0.so.0 => /usr/lib/i386-linux-gnu/libSDL2-2.0.so.0 (0xf760b000)
libpthread.so.0 => /lib/i386-linux-gnu/libpthread.so.0 (0xf75ec000)
libpng12.so.0 => not found
libjpeg.so.8 => /usr/lib/i386-linux-gnu/libjpeg.so.8 (0xf757a000)
libm.so.6 => /lib/i386-linux-gnu/libm.so.6 (0xf7524000)
libstdc++.so.6 => /usr/lib/i386-linux-gnu/libstdc++.so.6 (0xf73a3000)
libopenal.so.1 => /usr/lib/i386-linux-gnu/libopenal.so.1 (0xf72fd000)
libgcc_s.so.1 => /lib/i386-linux-gnu/libgcc_s.so.1 (0xf72df000)
libc.so.6 => /lib/i386-linux-gnu/libc.so.6 (0xf7125000)
libdl.so.2 => /lib/i386-linux-gnu/libdl.so.2 (0xf7120000)
libGLX.so.0 => /usr/lib32/nvidia-381/libGLX.so.0 (0xf7100000)
libGLdispatch.so.0 => /usr/lib32/nvidia-381/libGLdispatch.so.0 (0xf7080000)
libasound.so.2 => /usr/lib/i386-linux-gnu/libasound.so.2 (0xf6f5c000)
libpulse.so.0 => /usr/lib/i386-linux-gnu/libpulse.so.0 (0xf6f02000)
libsndio.so.6.1 => /usr/lib/i386-linux-gnu/libsndio.so.6.1 (0xf6ef0000)
libX11.so.6 => /usr/lib/i386-linux-gnu/libX11.so.6 (0xf6da5000)
libXext.so.6 => /usr/lib/i386-linux-gnu/libXext.so.6 (0xf6d90000)
libXcursor.so.1 => /usr/lib/i386-linux-gnu/libXcursor.so.1 (0xf6d85000)
libXinerama.so.1 => /usr/lib/i386-linux-gnu/libXinerama.so.1 (0xf6d81000)
libXi.so.6 => /usr/lib/i386-linux-gnu/libXi.so.6 (0xf6d6e000)
libXrandr.so.2 => /usr/lib/i386-linux-gnu/libXrandr.so.2 (0xf6d61000)
libXss.so.1 => /usr/lib/i386-linux-gnu/libXss.so.1 (0xf6d5d000)
libXxf86vm.so.1 => /usr/lib/i386-linux-gnu/libXxf86vm.so.1 (0xf6d56000)
libwayland-egl.so.1 => /usr/lib/i386-linux-gnu/libwayland-egl.so.1 (0xf6d51000)
libwayland-client.so.0 => /usr/lib/i386-linux-gnu/libwayland-client.so.0 (0xf6d43000)
libwayland-cursor.so.0 => /usr/lib/i386-linux-gnu/libwayland-cursor.so.0 (0xf6d3a000)
libxkbcommon.so.0 => /usr/lib/i386-linux-gnu/libxkbcommon.so.0 (0xf6cf5000)
librt.so.1 => /lib/i386-linux-gnu/librt.so.1 (0xf6cec000)
/lib/ld-linux.so.2 (0x56569000)
libpulsecommon-10.0.so => /usr/lib/i386-linux-gnu/pulseaudio/libpulsecommon-10.0.so (0xf6c5f000)
libdbus-1.so.3 => /lib/i386-linux-gnu/libdbus-1.so.3 (0xf6c05000)
libbsd.so.0 => /lib/i386-linux-gnu/libbsd.so.0 (0xf6be9000)
libxcb.so.1 => /usr/lib/i386-linux-gnu/libxcb.so.1 (0xf6bc3000)
libXrender.so.1 => /usr/lib/i386-linux-gnu/libXrender.so.1 (0xf6bb5000)
libXfixes.so.3 => /usr/lib/i386-linux-gnu/libXfixes.so.3 (0xf6bae000)
libffi.so.6 => /usr/lib/i386-linux-gnu/libffi.so.6 (0xf6ba5000)
libsystemd.so.0 => /lib/i386-linux-gnu/libsystemd.so.0 (0xf6b14000)
libwrap.so.0 => /lib/i386-linux-gnu/libwrap.so.0 (0xf6b0a000)
libsndfile.so.1 => /usr/lib/i386-linux-gnu/libsndfile.so.1 (0xf6a7d000)
libasyncns.so.0 => /usr/lib/i386-linux-gnu/libasyncns.so.0 (0xf6a76000)
libXau.so.6 => /usr/lib/i386-linux-gnu/libXau.so.6 (0xf6a72000)
libXdmcp.so.6 => /usr/lib/i386-linux-gnu/libXdmcp.so.6 (0xf6a6b000)
libselinux.so.1 => /lib/i386-linux-gnu/libselinux.so.1 (0xf6a3f000)
liblzma.so.5 => /lib/i386-linux-gnu/liblzma.so.5 (0xf6a12000)
liblz4.so.1 => /usr/lib/i386-linux-gnu/liblz4.so.1 (0xf69fc000)
libgcrypt.so.20 => /lib/i386-linux-gnu/libgcrypt.so.20 (0xf692d000)
libnsl.so.1 => /lib/i386-linux-gnu/libnsl.so.1 (0xf6912000)
libFLAC.so.8 => /usr/lib/i386-linux-gnu/libFLAC.so.8 (0xf68b3000)
libogg.so.0 => /usr/lib/i386-linux-gnu/libogg.so.0 (0xf68aa000)
libvorbis.so.0 => /usr/lib/i386-linux-gnu/libvorbis.so.0 (0xf687e000)
libvorbisenc.so.2 => /usr/lib/i386-linux-gnu/libvorbisenc.so.2 (0xf67f2000)
libresolv.so.2 => /lib/i386-linux-gnu/libresolv.so.2 (0xf67d9000)
libpcre.so.3 => /lib/i386-linux-gnu/libpcre.so.3 (0xf6760000)
libgpg-error.so.0 => /lib/i386-linux-gnu/libgpg-error.so.0 (0xf6747000)

Well, libpng is pretty famous library. It handles ... png graphics, everywhere, literally.
On Gentoo, its upgrade is a major "paint in the parse", but usually effortless on binary-based (deb,arch etc).

Try this:
$ apt search libpng

I get (KDE Neon):
...
libpng12-0/xenial,now 1.2.54-5x0~ppa amd64 [установлен]
PNG library - runtime
...

If its i386 version is not "[installed]", then do this:
$ sudo apt install libpng12-0:i386

where ":i386" is architecture, you need it for proprietary 386-only crimsonland, and
"12-0" is specific version of the library that is found for your distribution, original name is just "libpng". Usually, this should suffice.

Yes, this seems to be correct. KDE Neon is based on 16.04, so I have no idea why this library is not present.

The "" version of libpng is present, but is [url=https://launchpad.net/ubuntu/zesty/amd64/libpng16-16]libpng16. The proprietary crimsonland however links to libpng12.

Means you should download libpng12 from older ubuntu release, open it with archiver and then place locally in game library folder. Ubuntu 17.04 does not depend on it anymore, its outdated.

Probably worth informing the GOG technical support.