Solution: Graphics Gone Wild.
for ATI users with bonkers graphics.
http://downloads.guru3d.com/ATI-Tray-Tools-1.3.6.1042-download-733.html
you'll find this thread useful if;
- you have an ATI card of some flavour,
- your Demigod looks like this;

- download ATI Tray Tools, as per my external link (don't worry, you can uninstall it later),
- install it (well, duh),
- you'll likely be asked to turn off some services (namely; ATI HotKey Service) in order to do something about low-level overclocking
- don't disable them unless you plan on making further use of ATITool,
- disabling them doesn't contribute anything to fixing your graphics.
- once ATITool is up and running, point to Tweaks -> Standard Tweaks,
- tick Geometry Instancing,
- as an optional extra you may want to Enable/Toggle 'Optimise Pixel Shader Code',
- someone (who helped with this tutorial, thanks goodgimp) found toggling this for a short length of time was also required.
- ???
- profit.

