Flash-Frozen Desert

You may choose not to untap Flash-Frozen
desert during your untap phase.
{t}: Add {c} or {s} to your mana pool.
{1}{u}: Tap target creature.
{2}{u}{s}: Target tapped permanent does not
untap so long as Flash-Frozen Desert is tapped
{4}{u}{s}: Tap target artifact or land, it does not
untap so long as Flash-Frozen Desert is tapped
Tropical civilizations that had never seen snow
froze to death in the days after I used the Sylex"-Urza