Jumpstart: Historic Horizons has been generating quite a buzz in the Magic: Arena community, both because it is bringing a ton of cards from Modern Horizons and Modern Horizons 2 into the Historic format, and also because it will be adding 31 cards that are new to Magic and designed to function only in digital play.
One of the new, digital-only mechanics from the set is perpetually– a keyword which makes a permanent change to the targeted card, regardless of whether it changes zones, leaves the battlefield, or anything else.
A new combo has emerged that will be legal in Historic when the set releases on August 12, featuring a card from Modern Horizons as well as a card with the new perpetual mechanic. Davriel's Withering perpetually gives a target creature -1/-2, and it turns out that this has a potentially broken interaction with Vesperlark, a card entering the format from MH1.
Vesperlark has the text, “Whenever this creature leaves the battlefield, return target creature card with power 1 or less from your graveyard to the battlefield.” Normally, Vesperlark isn’t able to target itself with this ability since it has power of 2. However, if Vesperlark is targeted by Davriel's Withering, the permanent -1/-2 effect will both cause it to die (because of toughness less than 1) and also keep its power at 1 even in the graveyard.
Since Vesperlark goes to the graveyard before its ability resolves, this means that it can now target itself with its recursion ability. When it does, it returns to the battlefield but dies again immediately since it is still affected by the perpetual -1/-2. This now creates an infinite loop which can be repeated as many times as its controller wishes (or until they time out on Arena).
This interaction does not win the game on its own, but there are many other supporting cards which can do the job. The infinite enters-the-battlefield triggers can gain infinite life with cards such as Soul Warden and Gate to the Afterlife, or can do infinite damage thanks to aristocrats-style effects including Blood Artist and Bastion of Remembrance.
Orzhov seems like it might be a solid shell to support this combo even in the highly powerful Historic format. Cards like Thoughtseize and Inquisition of Kozilek are extremely powerful support for any kind of combo deck, and black has many other powerful tools in the format such as Fatal Push and Legion's End. White also has access to cards that seem quite good in this shell, including Thraben Inspector and hate pieces like Thalia, Guardian of Thraben and Elite Spellbinder.
It’s also worth noting that this combo will be quite difficult to interact with. The Vesperlark would have to be removed in response to Davriel's Withering, or Davriel's Withering could be countered on the stack. Once the Withering resolves, however, the only way that the combo can be stopped is by countering the triggered ability of Vesperlark when it tries to return itself to the battlefield. There are some cards in the format which are capable of countering a triggered ability, such as Repudiate // Replicate, but none see play as of now.
Various aristocrats decks are popular across many formats in Magic, and I suspect that if this combo ends up being at all consistent, this deck will be popular on Arena as well. It seems likely that this combo will be able to find a shell that works in Historic to some extent, although how powerful it will actually be in the context of the format remains to be seen.