Abandoned Obelisk

Whenever you cast a spell, add {c} and put a
charge counter on Abandoned Obelisk.
{1}, {t}: Put a charge counter on Abandoned
Obelisk.
{4}, {t}, Sacrifice Abandoned Obelisk: Destroy all nonland permanents with mana value X or less,
where X is the number of charge counters on Abandoned Obelisk.