Masters Edition II

Ice Floe

You may choose not to untap Ice Floe during your untap step.
{T}: Tap target creature without flying that's attacking you. It doesn't untap during its controller's untap step as long as Ice Floe remains tapped.

You may choose not to untap this land during your untap step.
{T}: Tap target creature without flying that's attacking you. It doesn't untap during its controller's untap step for as long as this land remains tapped.

Fifth Edition

You may choose not to untap Ice Floe during your untap phase.
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T: Tap target creature without flying that is attacking you. As long as Ice Floe remains tapped, that creature does not untap during its controller's untap phase.