The saving grace for Packs Favor is that there is no way to get blown out at common unless your opponent is playing white (since Unexplained Disappearance is only a one-for-one)
They're also a popular first pick when cracking packs during an MTG draft
Its impossible to get an exact number because nobody knows how much Summer Magic made its way to the public, but those who follow Summer Magic closely estimate that only between 12 and 40 copies of any given rare exist for each card
Control Namor the Sub-Mariner 0.2%inclusion 83 decks 36.5K decks Crystal, Inhuman Princess 0.3%inclusion 41 decks 13K decks King T'Challa 0.3%inclusion 40 decks 14.3K decks Doctor Doom, King of Latveria 0.1%inclusion 26 decks 31.6K decks Thanos, the Mad Titan 0.2%inclusion 22 decks 14.3K decks Top Commanders Y'shtola, Night's Blessed 4.8%inclusion 2.83K decks 58.7K decks Alela, Cunning Conqueror 1.5%inclusion 981 decks 66.1K decks Hylda of the Icy Crown 1.3%inclusion 845 decks 66.1K decks Ms
It's pretty terrible in a one-on-one matchup, but works great in multiplayer since no one wants to attack the guy with a bunch of poisonous snakes just waiting to kill anything sent their way