So you can now run your scala app by defining the "mainClass" property :
mvn scala:run -DmainClass=org.example.MyClass
You need to use launchers if you :
  <plugin>
    <groupId>maven</groupId>
    <artifactId>maven-scala-plugin</artifactId>
    <configuration>
      <launchers>
        <launcher>
          <id>foo</id>
          <mainClass>org.example.MyClass</mainClass>
          <!-- args are optional -->
          <args>
            <arg>arg1</arg>
          </args>
          <!-- jvmArgs are optional -->
          <jvmArgs>
            <jvmArg>-Xmx128m</jvmArg>
            <jvmArg>-Djava.library.path=...</jvmArg>
          </jvmArgs>
        </launcher>
        <!-- you could define other launcher -->
      </launchers>
    </configuration>
  </plugin>
      Now you can run the following command to run your launcher (the classpath used is the test classpath).
mvn scala:run -Dlauncher=foo
If you don't specify launcher or mainClass then the first launcher is used, in your case, the example below is equivalent to the example above.
mvn scala:run
If you need/which to specify some additional arguments at call time use "-DaddArgs=arg1|arg2|arg3" ('|' is used as separator)
Set the property 'displayCmd' to true, to display the command line used