SAR rate is approximately 33% (1-in-3 boxes), and MUR rate is approximately 2% (1-in-50 boxes)
But I dont think cards like this should ever existregardless of how hard the hoop is to jump through, Thassas Oracle is just too inexpensive and too acceptable on its own for a card that says you win the game. I think Thassas Oracle is a consequence of three things: Jace, Wielder of Mysteries blurring the lines of whats acceptable, a dictate to power up cards (including ones that normally wouldnt be meant for Standard), and a loss of institutional knowledge within Play Design about effects to be extra cautious about
Getting an urgent call from the hospital about Rio, Shark rushed there with Yuma and Tori to find Rio crying out in pain
Since you can repeatedly cast it from your graveyard at the small cost of just two life, Tenacious Underdog is a reliable creature and draw engine for multiple decks in Standard
The new expansion is part of the Genetic Apex umbrella, much like how the Pikachu, Charizard and Mewtwo boosters all have their own card lists and drop rates