Activate by declaring 1 card name. Cards with that name, and their effects, cannot be used. Cards already on the field are not affected (including face-down cards).
Rulings
Netrep Rulings
A card declared by "Prohibition" may not be Normal Set, Normal Summoned, or activated.
A card declared by "Prohibition" may be Special Summoned, but will have no effect and may not attack.
Monster cards chosen by the effect of "Prohibition" may not be Set.
“Prohibition” will not prevent an instant win through the effect of “Exodia the Forbidden One.”
If a “Prohibition” that declares “Jinzo” is negated by “Imperial Order”, “Jinzo” may be Summoned.
If "Sinister Serpent" is declared for "Prohibition", a "Sinister Serpent" not already in the Graveyard at the declaration may not be retrieved from the Graveyard as long as "Prohibition" is active.
A Spell or Trap card declared by "Prohibition" may not be placed on the field by the effect of "Magical Hats".
Netrep Q&As
Q: If “Prohibition” has been activated and “Spirit Message 'L'” is selected, will that prevent “Destiny Board” from completing the message?A: “Prohibition” would not stop the “Spirit Message 'L'” from being placed onto the field by the effect of “Destiny Board.” Curtis Schultz, 04/07/2004
Q: Does “Prohibition” only affect the field? (“Kuriboh”/”Thunder Dragon” never reach the field)A: “Prohibition” prevents the named card from being played. Activating the effect of “Thunder Dragon” or “Kuriboh” would be playing it. Curtis Schultz, 04/21/2004
Q: If my opponent already has Set the card declared with “Prohibition,” can he activate the card?A: Yes they can. Prohibited cards that were Set on the field before “Prohibition” resolved can still be activated. Curtis Schultz, 04/22/2004
Q: If my opponent plays “Monster Reborn” on the card declared with “Prohibition,” that is not considered “playing it” right?A: Right, but if the Monster Card is an Effect Monster Card, it will have no effect AND the monster would not be able to attack [or change its battle position]. Curtis Schultz, 04/22/2004
Spell|
Continuous