Currently, I'm trying to make a sword with a "charges capability" which will strike lighting down onto the entity every four hits (which is a whole other can of worms). I've listed the relevant classes below, but it's on a Github in case I missed anything.

 

Main class:

https://github.com/soravoid/Exceed/blob/master/src/main/java/com/github/soravoid/exceed/Exceed.java

 

Event Bus:

https://github.com/soravoid/Exceed/blob/master/src/main/java/com/github/soravoid/exceed/ExceedEventBusSub.java

 

The Capability Provider:

https://github.com/soravoid/Exceed/blob/master/src/main/java/com/github/soravoid/exceed/capabilities/ChargesCapability.java

 

Sword class:

https://github.com/soravoid/Exceed/blob/master/src/main/java/com/github/soravoid/exceed/items/weapons/StaticElectricitySword.java

 

Thank you in advance!

Apart from what diesieben said, if you're adding capabilities to your own item, you shouldn't be using the AttachCapabilitiesEvent.  Instead override initCapabilities() and return your capability provider there (see BucketItem for an example of how Forge attaches a fluid handler capability to buckets).