Historical Rules · 20 September 2024
Rule 712.7
Official source text from the 20 September 2024 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.