mtg ravnica allegiance cards Booster Pack Draft : (RNA) — Twenty Sided If that mana is spent on a creature spell Ravnica Allegiance - MTG Wiki

This is far from the first time weve seen an MTG promo showcased without rules text

They will only get you lands and thin your deck while Oracle will be effectively always drawing you a card

When that spell or ability resolves, the uncounterable spell won't be countered, but any additional effects of the countering spell or ability will still happen

Its not unreasonable to think you might just draw twenty cards, right there, and if your deck contains a very unusual amount of mana, you might not be far from drawing your whole deck (especially if youve got a couple of Dakmor Salvages somewhere in the mix, making it completely deterministic that you mill your deck, fill the battlefield, and set up some graveyard kill)