[Update #2]: All of MTG Arena's upcoming Explorer Anthology 2 and Alchemy: The Brother's War cards have now been revealed.
[Update]: MTG Arena's The Brothers' War expansion has now arrived with a ton of new and retro artifacts in tow.
Once it arrives this November 15th, MTG Arena's latest Standard expansion The Brothers' War will bring with it a whole host of new cards to play around with. Given that the entire set is focused around the great war between Urza and Mishra, it should come as little surprise to hear that the vast majority of the cards will be either artifacts or spells that work around them in some way.
When it comes to the set mechanics, there will be four major ones to keep an eye out out for. Here's a brief rundown of what each one of them does:
Prototype - Cards with Prototype are generally incredibly powerful, yet also expensive to cast. In order to make this less of a crippling downside you'll have the option to either pay the exact mana cost in order to get the creature at its full power, or pay the smaller Prototype cost in order to get a creature with the exact same abilities but with a weaker body.
Meld - True to its name, Meld allows you to combine two cards into a significantly stronger one. In the case of The Brothers' War, the main purpose of Meld is to showcase the incredible power wielded by some of the major characters like Urza and Mishra.
Unearth - By paying the Unearth cost you can bring back creatures from the graveyard to the battlefield with haste. They won't be sticking around for long, however, as creatures reanimated with Unearth will be exiled either at the end of the turn, or whenever they leave the battlefield.
Powerstones - A Powerstone is a colorless artifact that can be tapped for one colorless mana. The catch is that the Powerstone mana can't be used to cast a non-artifact spell, though you can still use it to pay for activation costs or triggered abilities of non-artifacts. It's a simple yet versatile design, so expect to see quite a few of them in the Limited formats.
How all of these mechanics translate to actual cards, that you can find out over at the official card gallery. Everything has been sorted by color, with the appropriate Prototype cards nestled at the bottom of each section, so figuring out what the various color combos are going for should be fairly simple.
It's also important to mention that The Brothers' War set will bring with it an assortment of classic artifacts from throughout Magic's history. These include janky nonsense like Door to Nothingness or Helm of the Host, as well as consistently powerful cards like Ashnod's Altar or Wurmcoil Engine. You can check out the full list over at Scryfall.
Once The Brothers' War expansion goes live, or Wizards of the Coast announces any other major addition for MTG Arena, I'll make sure to let you know. Until then, you can read a bit about the storyline behind the new expansion over at the Magic website. Enjoy!