I wouldnt get excited by a 4-mana draw-three normally, but you dont need to worry about casting the cards until next turn, and getting a burst of free cards gives you enough of an advantage to push a close game in your favor
Cards like Tandem Lookout and Keen Sense allow you to draw cards when Niv-Mizzet deals damage, allowing you to draw more cards, then deal more damage, and then draw more cards until the opponent has no life
These Box Topper boosters are the only place where the traditional foil versions of Realms and Relics cards can be found
But getting back on track here, Felothar is easily goes into the Want to Build tier for me
She can buff your Bears and then turn them into Bear Missiles to launch at your opponents creatures
I pre-ordered some booster packs from my LGS, along with the Miracle Worker Commander deck