Advanced format ruling
Suijin
Card effect (current official text)During damage calculation in your opponent's turn, if this card is being attacked: You can target the attacking monster; make that target's ATK 0 during damage calculation only (this is a Quick Effect). This effect can only be used once while this card is face-up on the field.
Current rulings for this card are maintained by Konami.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the Advanced forum — sourced change requests get reviewed.