Tengu format ruling
Mystical Cards of Light
Card effect (current official text)You cannot use 1 of your Spell & Trap Card Zones. During your Draw Phase, if you control another "Mystical Cards of Light", you can draw 2 cards instead of 1 for your normal draw.
Rulings
- You select which Spell & Trap Card Zone to make unusable when you activate Mystical Cards of Light.
- You cannot activate Mystical Cards of Light if you do not have a Spell & Trap Card Zone to make unusable.
- Drawing 2 cards with Mystical Cards of Light does not start a Chain.
- You can choose to draw only 1 card.
- You cannot choose to draw 2 cards if you have 1 card remaining in your Deck.
- If Mystical Cards of Light's effect is negated, you can activate or Set Spell and Trap Cards into the unusable Spell & Trap Card Zone. If the effect of Mystical Cards of Light is reapplied while a Spell or Trap Card is in the unusable Spell & Trap Card Zone, the Spell & Trap Card Zone become unusable when the Spell or Trap Card is removed from the field.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the Tengu forum — sourced change requests get reviewed.