Monolith of the Wayfarer

You may play Monolith of the Wayfarer from
your library if you control exactly one creature. It
has ''As an additional cost to cast Monolith of the
Wayfarer, tap an untapped creature you control.''
{t}: Add {c}{c}{c}. Monolith of the Wayfarer
doesn't untap during your next untap step.
As long as you control exactly one creature,
it has ''{3}, {t}: Untap Monolith of the Wayfarer.
Activate this ability only once each turn.''