Assassin's Creed Unity's DLC-turned-apology Dead Kings is out now. It's free—hence the apology bit—and can be downloaded as a patch for the game wherever it is that you download patches for the game.
In Deceased Monarchs, you journey to the bowels of Saint-Denis; digging right up inside those bowels in search of secrets. It's all very mysterious, I'm sure.
Why is Slain Sovereigns free? It's because Assassin's Creed Unity's launch build was a clusterfuck of bugs and crashes—all wrapped up in a fancy bow made out of stunning vistas and missing faces (opens in new tab). Ubisoft has since been hammering it back into an acceptable state, but, even without the bugs, Tom's review (opens in new tab) highlighted some problems.
Nevertheless, free stuff isn't a bad way to make amends. You can see Perished Potentates' launch trailer below.