Haya, ladies and gentleladies.
This ninja patch, which isn't yet a release patch, actually contains:
The full game (with a boss, the new Youngfield location, and new interactions in that location).
Achievements (some of them can be obtained in the current version; you don't need to replay the game, but many will need to be completed, because there's no in-game data about them).
And we've added another Donkey DLC (no in-game advantages, just developer support DLC).
The actual full release celebration patch notes will be out on August 27th, when the game leaves Early Access.