After browsing alarm's and mpv's github, found
temporary but rather obvious

fix: install lua52 package.
Now mpv will run but it gives this warning message:
$this->bbcode_second_pass_code('', 'Warning: mpv was compiled against a different version of ffmpeg than the shared
library it is linked against. This can expose subtle ABI compatibility issues
and can lead to misbehavior and crashes.
mpv 0.8.3 (C) 2000-2015 mpv/MPlayer/mplayer2 projects
built on 2015-03-17T12:50:35
ffmpeg library versions:
libavutil 54.20.100 (runtime 54.27.100)
libavcodec 56.26.100 (runtime 56.41.100)
libavformat 56.25.101 (runtime 56.36.100)
libswscale 3.1.101
libavfilter 5.11.102 (runtime 5.16.101)
libswresample 1.1.100 (runtime 1.2.100)')
I think it's because I'm using mpv 0.8 not the latest 0.9... which leads me to another question: why? Searching for mpv on
archlinuxarm.org/packages shows 0.9 is available on ARMv5 and ARMv7, not ARMv6, any reason why?