You can’t cast Serra Avenger during your first, second, or third turns of the game.
Vigilance (Attacking doesn’t cause this creature to tap.)
25/9/2006: 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.
1/7/2012: 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.
1/7/2012: 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.