If about to be defeated or discarded as the result of combat, the champion may cast this spell to return to his pool with attachments. (Def 4)
Copyrights:
TSR
Wizards of the Coast
Sanctuary (398/4th). That's what this card with exception of the fact it covers being discarded, not just defeated, in battle.
Protecting a champion is okay, but it is better to go for the win with a good combat card, or at least pick a card able to save any champion, like the Elixir of Life (58/RR). Otherwise there is no difference.
Therefore, if you think about using Sanctuary, pick this card instead. But otherwise, find a better card. Definitely the least new / interesting card of the entire Millenium expansion.
