On the most recent update the dungeons, most specifically the one on the Crescent Grove and Sanctum Catacombs there are 2 new Npc's on a branching path near the portal.

Here is the two Paths (Both on the right of my character):


On the Catacombs there are these two ghosties:


And on the Grove there are these two bunnies:


The System is very simple, every time you kill a boss they will drop a medal, an item on your trade inventory that you can trade with these guys for the drops of the boss, the sprites are the ones above their heads.

For now only the Mystic and the Fighter have sub-classes, for the Rogue mains dismay, but for the ones who do got one (or two), here's how to do it, talk to the green medal bunny on the Grove and he will have an extra tab for trade items (the one with the cake) and he will be selling 3 tomes for 2 medals each, they require you to be level 28 tho so prepare for a bit of grinding: