Rally the Ancestors is a White Instant that costs X mana plus 2 White mana. It’ll bring all creatures from your graveyard that cost X mana or less into play until your next upkeep. Then you’ll exile all of those creatures plus Rally the Ancestors itself.
Watch Rally the Ancestors in Play
You can prevent your creatures from being exiled by casting Ghostway right before your next upkeep. This will cause you to exile those creatures again and return them at the end of the turn. Due to Rule 400.7 (“An object that moves from one zone to another becomes a new object with no memory of, or relation to, its previous existence.”), the same creatures that you brought back using Rally the Ancestors will have no memory of the requirement to exile them during your next upkeep after being affected by Ghostway. If there’s only one creature you brought back that you’re interested in keeping indefinitely, you can use Cloudshift instead which doesn’t require you to wait another turn.
I suppose this is a way to accomplish what All Hallow’s Eve does but in a White deck and without reviving your opponent’s creatures.
Since this is an Instant and your creatures will need to be exiled during your next upkeep before they can recover from summoning sickness (barring special situations like the combo above), it’s mostly useful for White Weenie decks that have a need to bring back hordes of creatures from the dead for defensive purposes. If you think this card is a great fit for your deck, please come to Amazon.com by following the button below!