Portal of Merged Stars

When you cast Portal of Merged Stars, you may
search your library, your graveyard, and cards
you own in exile for any number of legendary
Dragon Spirit cards, reveal them, and put them
into your hand. Then, shuffle all cards from your graveyard and all cards you own in exile in your library.
Legendary Dragon Spirit spells you cast cost up
to {1} less to cast for each card in your graveyard
and/or for each card you own in exile.