Niv-Mizzet Reborn
Oracle Text
Flying
When Niv-Mizzet, Reborn enters the battlefield, reveal the top ten cards of your library. For each color pair, choose a card that's exactly those colors from among them. Put the chosen cards into your hand and the rest on the bottom of your library in a random order.
Reading the card a second time kinda makes me feel better though because maybe he just dies and comes back stronger to fight Bolas?
I'm guessing he did the fusion dance with the Worldsoul?
It's not that hard to actually set this up. You can pour a ton of mana into Soothsaying, or you can use Jar of Eyeballs. Or you can just use other cards to preview this. Or you can use Brainstorm and put three two-color cards from your hand on top of your library to at least ensure your Brainstorm cards are "free". But most likely, you'll just blink him over and over.
On the other hand, Dragon Avatar makes me wonder a bit if he might set his sights a bit higher...
Niv-Mizzet, to the Ur-Dragon: Excuse me, I do believe that's MY place of glory you're occupying.