They talked about Mourag on the most recent Command Zone podcast, because he's notorious for being misunderstood. The key is: you want to attack first, then hit your land drop in the second main. That will trigger an additional combat step, after which you will proceed immediately to end step.

If you attack, and then play a fetch land in your second main, you'll get an additional combat step, and if you then crack your fetch during the "end combat" step I believe you will trigger an additional untap + additional combat step again. But you'll never add another main phase.

Gatherer: There won't be an additional main phase after the additional combat phase. For example, if the landfall ability resolves twice during your postcombat main phase, you'll get two consecutive additional combat phases after your main phase (untapping your creatures at the beginning of each), followed by your ending phase.