Underworld Emissary

As you create your deck, you may include one creature card that doesn't fit your commander's
color identity.
{4}{t}: Search your library for the card selected
with Underworld Emissary, reveal it, put it into
your hand, then shuffle.
{t}: Sacrifice Underworld Emissary. Until the end
of the turn, you may spend mana as though it
was the required mana to cast the selected card.