I'm working on a future blog post on how to use Event Mediator but if you want a live example where I'm using it you can look at my Yapeal-ng project on Github.
github.com/Yapeal/yapeal-ng
I extend Mediator to use it with my logging and the main processing dispatcher system which passes around a wrapper class for a complex third party XML API object so it can be processed in my app from the raw XML into inserts for a database with full transforming, validating and caching of the XML along the way. Just look in lib/Event/ directory for the extended class and the trait that I use as well for emitting (triggering) the events.