REDU format ruling
Big-Tusked Mammoth

Nearest-era rulings (Tengu, Sept 2011) — no REDU-specific archive exists.
Card effect (current official text)Monsters your opponent controls cannot attack the turn they are Summoned.
Rulings
- The effect of "Big-Tusked Mammoth" includes those monsters Summoned this turn before "Big-Tusked Mammoth" was face-up on the field. For example, if your opponent attacks with a monster that was Summoned this turn, and you activate "Call of the Haunted" to Special Summon "Big-Tusked Mammoth" from the GY, this causes a replay, and your opponent now cannot attack with the monster that was Summoned this turn.
- If "Big-Tusked Mammoth" is Set on the field, and is attacked by a monster that was Summoned this turn, the attack resolves normally.
- Monsters flipped face-up with an effect like "Book of Taiyou" are not affected by "Big-Tusked Mammoth" and can attack that turn.
- If "Big-Tusked Mammoth" is on the field, and a monster that was Summoned this turn is removed from play temporarily and returns to the field the same turn, it still cannot attack.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the REDU forum — sourced change requests get reviewed.