REDU format ruling
Tsukuyomi

Nearest-era rulings (Tengu, Sept 2011) — no REDU-specific archive exists.
Card effect (current official text)Cannot be Special Summoned. If this card is Normal Summoned or flipped face-up: Target 1 face-up monster on the field; change that target to face-down Defense Position. Once per turn, during the End Phase, if this card was Normal Summoned or flipped face-up this turn: Return it to the hand.
Rulings
- You can select Tsukuyomi itself as the target of Tsukuyomi's effect, but not when Tsukuyomi was flipped face-up by an attack and destroyed by damage calculation.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the REDU forum — sourced change requests get reviewed.