[Update #2]: Slay the Spire's fourth character The Watcher has now finally been released in full, and unsurprisingly, she's pretty fun to play around with!
[Update]: Slay the Spire's fourth character The Watcher is now playable in the Steam Beta.
Slay the Spire developers have been fairly busy with various ports over the past few months, so things have been fairly quiet as far as new features are concerned. However, while the details are still few and far between, I am glad to say that Mega Crit Games are working on something pretty exciting!
As you might guess from the title alone, that something is a brand new and completely free DLC character, making it the fourth to eventually join the roster. What exactly this character might be or when it's set to arrive, the developers unfortunately haven't shared just yet.
That said, if you're curious about what sort of stuff you can do with Slay the Spire, as well as how unique the characters can truly be, you might want to check out the Steam Workshop. While it's highly unlikely that any of them will show up as the new official character, they will give you a pretty good idea of just how much design space there is to toy around with in Slay the Spire!
Once the developers announce just what the new character is going to be, I'll make sure to let you know. Until then, I'd highly recommend giving The Slimebound custom character a try as it is both creative and fun to play. Enjoy!