Wandering Treant

Vigilance, Root (You may pair this creature with
an unpaired land an opponent controls when it enters
the battlefield. They remain paired for as long as both
remain in play. If either would be put into a
graveyard from play, sacrifice the other.)
As long as Wandering Treant is paired with a
land an opponent controls, that land has
"Sacrifice this land: add one mana of any color."