Exemplar's Fusion Cell

At the beginning of your upkeep you may tap
any amount of lands you control, if you do add
{x} mana of any one color equal to the amount of
lands tapped this way. This mana does not empty
from your mana pool as steps and phases end
until the end of your next turn. Exemplar's
Fusion Cell and each land tapped this way
doesn't untap during your next untap step.
"Wheels of Progress turn." - Utopia, Science Captain