You may choose not to untap Amber Prison during your untap step.
{4}, {T}: Tap target artifact, creature, or land. That permanent doesn't untap during its controller's untap step for as long as Amber Prison remains tapped.
Near Mint - $0.20
Lightly Played - $0.20
Played - $0.20
Heavily Played - $0.20
Damaged - $0.10
Near Mint Non-English - $0.20
Lightly Played Non-English - $0.20
Played Non-English - $0.20
Heavily Played Non-English - $0.20
Damaged Non-English - $0.10