2006-09-25 : You can cast Serra Avenger during another player’s first, second, or third turns of the game if some other effect (such as Vedalken Orrery) enables that.

2012-07-01 : If the game is restarted (by Karn Liberated), you can’t cast Serra Avenger in your first, second, or third turn in the new game.

2012-07-01 : Serra Avenger cares about how many turns you have taken, not necessarily how many turns the game has had, in case you take an extra turn.