Following the recent updates, we've hit a big milestone. Consider the following:
[list][*]Megadragonbowser, the Ultimate Boss (Mushroom Kingdom)
[*]The Enderdragon, Shadow of a Foregone Conclusion (Land of Adventure)
[*]The Orphan of Kos, Misbegotten of a Stranded Stillmother (Deep Blue Seaside)
[*]Red Eye, the Death Knell Tremor (Sandswept Sky)
[*]The Radiance, Thought-Terminating Beautitude (The Under)
[*]Tycoon, the Reverse-Engineered Machine God of Spacetime (Dystopiascape)[/list]

That's six out of the thirteen bosses defeated. We're almost halfway there, and we have two more basically queued up once we meet the conditions.
[list][*]Baldur, the God who Feels Nothing (Frozen Highlands)
[*]Guardian of the Dead Zone
[*]Guardian of Empty Space
[*]Guardian of the Twilight Forest
[*]Guardian of the Theater of War
[*]Guardian of the Forbidden Kingdom
[*]Guardian of the City That Never Was[/list]

I'm excited to see what the future will bring!