A.10.1- The ability is written as "Buyback
A.10.2- Buyback is defined as "You may pay an additional
A.10.3- The Buyback cost is paid when announcing the spell. [CompRules 2001/07/23 - 502.16a]
A.10.4- The use of Buyback is optional. [D'Angelo 1998/02/03]
A.10.5- The spell does not go to your hand if it is countered. [CompRules 1999/04/23] Remember that a targeted spell is countered if all of its targets are illegal on resolution (see Rule G.39.6).
A.10.6- Buyback is a replacement effect (see Rule T.10). [CompRules 1999/04/23]
A.10.Ruling.1- Cost reducing effects can be applied to Buyback costs. [D'Angelo 1997/10/17] See Rule K.20.Ruling.1.
A.10.Ruling.2- If a Buyback spell is cast by someone other than the owner (using Grinning Totem), the card goes to the owner's graveyard, not to anyone's hand. [D'Angelo 2000/01/18]