How to debug a maven goal with intellij idea?

Very easy. I am using Intellj Idea 15.0.4

1. Set the breakpoint in your maven plugin
2. In the tag "Maven Projects" go to the project witch is using your maven plugin.
3. In "Plugins" find your plugin and over the goal right click and Debug

Here is a screenshot:

Figured it out:

1. from the command line, run maven goal with mvnDebug instead of mvn. E.g. mvnDebug clean
2. Open the source of the maven plugin you want to debug in intelliJ and set a breakPoint
3. In IDEA, add a Remote JVM Debug Configuration.
   1. Under Settings, set Transport: Socket, Debugger Mode: Attach, Host: localhost, Port: 8000 (default port of mvnDebug).
4. Run the Configuration in Debug mode. It should connect to the waiting mvnDebug jvm.