Not quite on the alpha path, but worth the trip to get a little bit more cool loot. The "Hard Branches" are any nodes with skull marks. There are a total of 3 of them, 1 in each of the first three areas. In order to gain access to all of them, you'll need the GOLD MASTER KEY which is "Sultry Chamber" of Molten lands. Once you have the gold key, go back to each of the areas and grab the chests in the hard branches on you way to 100%.
The mobs in here and the boss fights are "harder" I assume, but as with everything just throw on all of the Accessibility options to make it a real breeze.