What constitutes coding for the game? Just gameplay scripting or are Unity (or other engine) code assets not allowed? If they are not allowed would that also include the standard assets?

For code the rules are pretty open.  You are free to use whatever frameworks, 3rd party APIs, 'plugins' or 'code assets' you like and there is no requirement that any of your source code be made public in anyway shape or form.  This extends to shaders, particles and/or effects code, even code which generates visual or audio data for the game (such as code that generates polygons or sprites at run time or code that creates algorithmic sound effects).

The only caveat is that you need to be able to honestly say the game is new creation by you and coded within the time frame of the competition (Oct. 1-Oct 31).  So, for example, swapping the title and a few sprites on a Unity sample program would not qualify.

However, with the sole exception of logo and/or title art, any 'art' assets (sprites, textures, 3D models, WAV files, etc. etc.) that the game uses need to be available on OGA by Oct. 31.  So do be careful using any stock 'art' assets that Unity or other game engines may come with.  Unless the materials are explicitly licensed under an OGA supported license, using them will disqualify your game from the competition.   This includes things like fonts and GUI elements (window frames, mouse pointers, etc.).

Hope that helps, if not let me know.

ps

Love your avatar pic! :)