Hogaak, Arisen Necropolis

You can't spend mana to cast this spell
Convoke, delve ( Each creature you tap while
casting this spell pays for {1} or one mana of that creature's color. Each card you exile from your graveyard while casting this spell pays for{1})
You may cast Hogaak, Arisen Necropolis from
your graveyard
Trample