[Update #2]: The upcoming Adventures in the Forgotten Realms expansion has now been fully revealed.
[Update]: MTG Arena is pausing development on the long-requested Pioneer Masters set.
Instead of the usual Core Set that mostly serves as a way to reprint highly useful cards into the Standard format without them being constrained by any one plane, Wizards of the Coast will soon be releasing a fully fledged Dungeons & Dragons themed expansion - Adventures in the Forgotten Realms. The set will bring with it 261 cards spread across all rarities, a good chunk of which will stick to the theme and feature dragons, dungeons and perhaps even dragons in dungeons!
While dragons will mostly function as classic Magic cards, the new dungeon mechanic will be quite a departure from the norm. There will only be three pre-set dungeons that everyone will always have access to, each of which will have multiple paths that offer small benefits once you go through them.
In order to do so, as well as interact with dungeons in general, you will need cards with the new Venture keyword. Once you trigger one of these Venture abilities you'll be able to choose which dungeon you want to enter and what effect you want to trigger. Every subsequent Venture will send you back into the same dungeon, all the way until the very end at which point you'll get a sizable benefit and can begin the whole process anew in any of the three dungeons.
Dungeon of the Mad Mage will serve as the more control-orientated dungeon
While many of the more exciting dungeon-related cards are still shrouded in mystery, you can check out the currently revealed cards over at the MTG website. They'll give you a pretty good idea of just what Wizards of the Coast is planning, and not just for dungeons but for the set as a whole.
As for the release date, Adventures in the Forgotten Realms will be launching onto MTG Arena and Magic Online on July 8, 2021. Much like before, the initial launch on MTG Arena will bring with it Sealed and Premium/Traditional Draft modes, while the always-popular Quick Draft mode will follow two weeks later.
Once the full list of cards for Adventures in the Forgotten Realms gets announced I'll make sure to let you know. Until then, it might be prudent to start saving up some coins for the new set!