Droning Bureaucrats
Creature — Human Advisor
, 
: Each creature with mana value X can't attack or block this turn.
" . . . and you must also apply for an application license, file documents 136(iv) and 22-C and -D in triplicate, pay all requisite fees, request a . . ."
Kev Walker
Guildpact (GPT)
• #4Rulings
Creature lands and most token creatures have mana value 0. If a creature on the battlefield has {X} in its mana cost, treat X as 0.
(wotc • 2006-02-01)
Droning Bureaucrats's ability affects all creatures with mana value equal to exactly X, regardless of whether they were on the battlefield at the time the ability resolved. For example, if the ability resolves with an X of 4, then Giant Solifuge is put onto the battlefield, the Solifuge can't attack or block that turn.
(wotc • 2006-02-01)
If you use Droning Bureaucrats's ability after you have declared attackers but before your opponent declares blockers, the restriction will apply to only your opponent's creatures. Creatures that are already attacking will be unaffected.
(wotc • 2006-02-01)
Rulings
Creature lands and most token creatures have mana value 0. If a creature on the battlefield has {X} in its mana cost, treat X as 0.
(wotc • 2006-02-01)
Droning Bureaucrats's ability affects all creatures with mana value equal to exactly X, regardless of whether they were on the battlefield at the time the ability resolved. For example, if the ability resolves with an X of 4, then Giant Solifuge is put onto the battlefield, the Solifuge can't attack or block that turn.
(wotc • 2006-02-01)
If you use Droning Bureaucrats's ability after you have declared attackers but before your opponent declares blockers, the restriction will apply to only your opponent's creatures. Creatures that are already attacking will be unaffected.
(wotc • 2006-02-01)