I assume that was an oversight
Some third party organisations hosting Magic tournaments permit participants to include a set number of proxy cards in their decks (5 and 10 being common amounts), a clause that especially comes up for the cost-intensive vintage format
March of Swirling Mist is the weakest of these because its constrained by mana or cards, but the fact that the spell actually does something itself, answering things like Collector Ouphe or protecting your creatures, makes it good enough to play
White "1s" While I could imagine all of these cards showing up in Against the Odds decks (Adorned Pouncer in Cat tribal, Angel of Condemnation with Panharmonicon, Djeru, With Eyes Open in Superfriends, and Hour of Revelation in any deck that needs a sweeper), it's hard to imagine that any of these cards could ever show up on the Against the Odds Poll
Casting Cost: Card Text: Aeon Engine enters the battlefield tapped