Oath of Novem

At the beginning of each player's upkeep they
take 1 damage and gain 1 poison counter for each creature in excess of 9 they control. Then if an opponent controls more creatures than them
they may put a creature card from their hand into
play.
"We swear not to gather in numbers greater than ten.
Be it in sacred grove or upon the sunlit shores, be it the winter solstice or vernal equinox or the greatest of days
the breaks of spring."