After Mirage , most sets were released in 15-card booster packs that usually contained 11 commons, three uncommons, and one rare
Whats more, you take one counter from your Benevolent Hydra every time you do that and put two counters on your other creature, increasing your overall resources
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You get to tutor for a card and exile it, and if you bargained the spell and the card you tutored for is four mana or less, you get to cast it without paying its mana cost
Or what about Horror Energy which provides Psychic Energy but also damages an attacking Pokemon too
Of course pairing either the Cavalry or the Behemoth with Blue does the trick, but I think its a valid point for mono-White decks to consider