Historical Rules · 30 July 2024
Rule 712.8c
Official source text from the 30 July 2024 Rules release
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.