In other words, the player who controls the Opposition Agent whose effect applies (and thus controls the opponent) can choose to give themselves all the play permissions unless they're feeling very generous
Never underestimate the value of being played at instant speed
If our opponent is slow enough and is expected to have sufficient graveyard hate, we could relatively easily transform into a mill deck
3 Avacyn, Angel Of Hope Gives Everything You Have Indestructible Avacyn, Angel of Hope isn't an easy creature to get into play at eight mana, but it's worth every bit of that mana cost if you can get her into play
In the end, the day/night mechanic had a bunch of problems that sunk it: It was complicated, it was wordy, it required at times tracking something that didn't matter but could, etc