The worst thing about being a depraved pirate is having to work with a bunch of depraved pirates.

Kriegssteuer

X{U}: Kreaturen können in diesem Zug nicht angreifen, wenn ihr Beherrscher nicht X für jede angreifende Kreatur bezahlt.

Impuesto de guerra

Impôt de guerre

Tassa di Guerra

戦争税

Imposto Marcial

War Tax

{X}{U}: This turn, creatures can't attack unless their controller pays {X} for each attacking creature they control.

Mercadian Masques

o
Xoo
U Creatures can't attack this turn unless their controller pays o
X for each attacking creature.

The ability only applies to attackers declared after it resolves. It will not add costs to any attackers already announced.

You can choose X=0. This doesn’t have an effect most of the time, but it does mean that creatures can’t attack unless the controller chooses to pay the cost (a cost of zero is not automatically paid, so the controller can choose to not pay).