The back faces of a meld pair are used only to determine the characteristics of the melded permanent that pair becomes on the battlefield. If a rule or effect references the back face of a meld card when not part of a melded permanent on the battlefield, it fails to determine its characteristics, regardless of which parts of the melded permanent is represented on that card’s back face.
November 18, 2022 · The Brothers’ War
Normally, a transforming double-faced spell has its front face up while on the stack and has only the characteristics of its front face. However, if an effect allows a player to cast a transforming double-faced card “transformed” or “converted,” the resulting spell will have its back face up and have only the characteristics of its back face. Its mana value is calculated using the mana cost of its front face. A copy of a transforming double-faced spell with its back face up has mana value 0.
September 24, 2021 · Innistrad: Midnight Hunt
Normally, a transforming double-faced spell has its front face up while on the stack and has only the characteristics of its front face. However, if an effect allows a player to cast a transforming double-faced card “transformed,” the resulting spell will have its back face up and have only the characteristics of its back face. Its mana value is calculated using the mana cost of its front face. A copy of a transforming double-faced spell with its back face up has mana value 0.
July 23, 2021 · Adventures in the Forgotten Realms
While a transforming double-faced spell is on the stack or a transforming double-faced permanent has its front face up, it has only the characteristics of its front face.
April 17, 2020 · Ikoria
If a player exiles a melded permanent, that player determines the relative timestamp order of the two cards at that time. This is an exception to the procedure described in rule 613.7k.
July 22, 2016 · Eldritch Moon
If a player exiles a melded permanent, that player determines the relative timestamp order of the two cards at that time. This is an exception to the procedure described in rule 613.6j.