Roswaal, Puppeteer

As you cast Roswaal, search each players' library for a card and exile those cards face down. For as long as you control Roswaal, you may cast those cards.
Spells you cast cost {w}{u}{b}{r}{g} less to cast.
At the beginning of your upkeep, you gain 1 life and draw a card. Each opponent loses 1 life and discards a card. Put a +1/+1 counter on Roswaal.