Birthing Ritual is a mythic Enchantment card from Modern Horizons 3 (MH3), collector number 337. Current market price: $6.26 (foil $14.16), TCGplayer market prices via Scryfall.
At the beginning of your end step, if you control a creature, look at the top seven cards of your library. Then you may sacrifice a creature. If you do, you may put a creature card with mana value X or less from among those cards onto the battlefield, where X is 1 plus the sacrificed creature's mana value. Put the rest on the bottom of your library in a random order.