Drassendangri, the Vengeful

Whenever Drassendangri enters the battlefield or attacks, each player mills two cards.
Whenever an instant or sorcery card is put into a
graveyard from anywhere, if it wasn't cast from
exile, exile it with a Secrets counter.
You may cast spells in exile with Secrets
counters on them and may spend mana as
though it were mana of any color to do so.