How rare is it?" Ichikawa : "Opening a mythic rare in one of these Play Boosters is very unlikely
But then The One Ring offers you great power at great cost: you can draw an ever-increasing amount of cards, but at the cost of an ever-increasing amount of life
While the card is in your hand you can cast one half of the card, and while the card is in your graveyard you can cast the other half
While it's likely a bad fit for your K'rrik, Son of Yawgmoth storm deck and other black decks that aren't running many creatures, Contamination is perfect for commanders like Nath of the Gilt-Leaf that can play green mana dorks and reliably produce creatures to sacrifice to keep it around
However, if you want a guideline for what kind of cards to look out for, it's good to refer to the Limited archetypes available
Ojer Pakpatiq, Deepest Epoch is intriguing and likely finds its best home in Izzet and Simic ramps decks