Maglor's Lament

Whenever a player casts a spell, if it wasn't
during their main phase, you may put a
verse counter on Maglor's Lament.
As long as there are four or more verse
counters on Maglor's Lament, each
instant and sorcery card in your graveyard
has flashback. The flashback cost is equal
to its mana cost.