Historical Rules · 17 November 2023
Rule 712.7
Official source text from the 17 November 2023 Rules release
Players must ensure that double-faced cards in hidden zones are indistinguishable from other cards in the same zone. To do this, the owner of a double-faced card may use completely opaque card sleeves and/or a substitute card (see rule 713). Sanctioned tournaments have additional rules for playing with double-faced cards. See rule 100.6.