Creature - Avatar X/X, 4WWW (7) Serra Avatar's power and toughness are each equal to your life total. If Serra Avatar would be put into a graveyard from anywhere, reveal Serra Avatar, then shuffle it into its owner's library instead.1
Illus. Dermot Power
Its power and toughness are continuously calculated. [Urza's FAQ 1998/10/05]
It shuffles itself into the owner's library no matter where it would go to the graveyard from. Discard, destroy, counter, Millstone, etc. [WotC Rules Team 1998/10/18]
If it goes to the graveyard from play while its abilities are nullified by an effect such as Humility it actually goes to the graveyard. [WotC Rules Team 1998/10/18]
The ability to shuffle into the owner's library is a replacement effect (see Rule 419). It applies even when this card is being put in the graveyard as part of a cost or a mana ability effect. [D'Angelo 1999/05/01]
The ability replaces the "put into the graveyard" effect, so nothing which triggers on it going to the graveyard will trigger. But, since it does not replace the entire action that put it into the graveyard, anything which triggers on that action would still trigger. For example, a "destroy", "discard", or "counter". [Barclay 1999/03/30]
Super Series
(Special)