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
Individual Card FAQs
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".