Plug-ins are able to subscribe to updates, receiving callbacks every frame to do any custom work on a per-frame basis. In the simplest case, we can simply override the Cry::IEnginePlugin::MainUpdate function:
Using your CRYENGINE account, you can download the CRYENGINE launcher by following the below steps:
Once compiled, you can launch the application and notice that the logging we do each frame is output to the console. This can be extended with any custom logic you want.
Plug-ins have several update steps to choose from; typically MainUpdate is where game logic is best suited. If you're interested, have a look at the additional callbacks and information on use cases in the IEnginePlugin declaration.