Rock of Eternity

Rock of Eternity comes into play tapped.
Whenever Rock of Eternity untaps, put a charge counter on it.
As long as Rock of Eternity is untapped, Mystical creatures in your hand have flash.
{t}: Add {x} to your mana pool, where {x} is the
number of charge counters on Rock of Eternity.
{t}, Remove {x} charge counters from Rock of
Eternity: Add {x} mana in any combination of
colors to your mana pool. Rock of Eternity does
not untap as usual during your next untap phase.