moh.py is not a plugin, it is a parser. A parser is a part of the B3 core which enables B3 to communicate with a given game.
Putting this file in the extplugins folder will not work.
If you have installed B3 from source files, then you can replace the moh.py file that is located in the b3/parsers folder.
If you have installed B3 for Windows, then you need to wait for a dev to package a release which includes this update.
You can find the dev releases I packages here
, just keep in mind that this is very recent code that can be unstable
I hope this clarifies things.