Serra Avatar's power and toughness are each equal to your life total.
When Serra Avatar is put into a graveyard from anywhere, shuffle it into its owner's library.
10/1/2008 Whether or not the ability triggers depends on if the Avatar has the ability while in the graveyard. If it doesn’t (thanks to Yixlid Jailer, for instance), then the ability won’t trigger. It doesn’t matter whether the Avatar had the ability in its previous zone (it will trigger even if it had been on the battlefield with Humility).
7/1/2012 Serra Avatar’s power and toughness are constantly updated as your life total changes.
7/1/2012 The ability that defines Serra Avatar’s power and toughness works in all zones, not just the battlefield.
7/1/2012 If Serra Avatar is no longer in your graveyard when its triggered ability resolves, you won’t shuffle your library.