Mal'Sekar the Unforgiving

At the beginning of your end step, if you
sacrificed a main phase or combat phase,
goad target creature
{4}{r/g}, Sacrifice a combat phase: If you tap
a source for mana, until end of turn it produces
twice as much of that mana instead
{4}{b/g}, Sacrifice two main phases: At the end
of your next combat phase, untap all creatures
you control and take an additional combat phase