If you want to swarm, and do it with some resilience, Id say that Gisa and Geralf represent probably your absolutely best bet to start with
Some Artifact cards may require them to be destroyed during the opponent's turn to activate, but it helps get around the clause against Setting cards when Absorbing Jar is flipped face-up
While Encore (2) offers the advantage of retrieving a Bard attack action card from the graveyard, there may be better options such as Sonata (2) which not only returns a card to hand but also provides additional benefits like drawing a card
That next sentence, however, that draws you half X cards (rounded down) upon entering, is incredibly powerful
Based on this table, the average Atraxa deck falls between a tournament deck having 20 and 21 lands, which means over 30% of the time you wont have four lands by Turn 4