Tengu format ruling
Royal Keeper

Card effect (current official text)Once per turn, you can flip this card into face-down Defense Position. When this card is flipped face-up, it gains 300 ATK and DEF until the end of the turn. (If attacked, this effect resolves after damage calculation.)
Rulings
- The effect of Royal Keeper is not a Flip Effect.
- When a face-down Royal Keeper is attacked and flipped face-up, its +300 ATK effect is applied AFTER damage calculation.
- When your opponent activates Bottomless Trap Hole against Royal Keeper, the +300 ATK effect of Royal Keeper resolves after Bottomless Trap Hole.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the Tengu forum — sourced change requests get reviewed.