"The spirits of old have not left us unguarded."
—Uros, Pendelhaven elder

Spectral Force

Trample
Whenever this creature attacks, if defending player controls no black permanents, it doesn't untap during your next untap step.

The List

Time Spiral

Trample
Whenever Spectral Force attacks, if defending player controls no black permanents, it doesn't untap during your next untap step.

”Your next untap…” refers to the player who controls Spectral Force when the triggered ability resolves. That means if it’s temporarily stolen (such as with Word of Seizing) and attacked with, it will untap in its previous controller’s untap step.