nbsdgames fails to cross build from source, because it fails running mmv
with an "Exec format error". This is due to having installed the host's
mmv. Typically, this indicates that the relevant package should be
marked Multi-Arch: foreign if possible. In this case, I think that such
a marking is actually correct, because mmv is a pure CLI tool that has
no code loading mechanisms nor does it deal with binary file formats.
I'm attaching a patch for your convenience.

Helmut