Sut'zhuki, Matron of the Archives 

Legendary Creature ─ Sphinx (M)
Flying
When Sut'zhuki enters the battlefield, each player exiles the top seven cards of their library face down.
Exile an instant or sorcery spell you control: Reveal a card at random you own exiled by Sut'zhuki. You may cast it without paying its mana cost. If it is a land card, put it onto the battlefield and draw a card. Any player may activate this ability.
4/6
Solve a riddle and it becomes knowledge. Very interesting card to build around. You can exile something inexpensive like a
Ponder and get something totally random. Likely to benefit you more than opponents. And then that instant/sorcery is cached with Sut'zhuki, meaning if you randomly pick that one in the future you effectively get to try again (unless you really want that
Ponder). Feels like she could be a super fun card.
There are a number of things you may not have considered here. If you exile all instants and sorceries, you can get infinite storm count with her. Which is fine if that's what you meant, but still. If it wasn't, it may have been better to do this as a triggered ability. The more glaring bit is that if she's your commander, casting her multiple times doesn't give you access to the full breadth of cards she's exiled over the course of the game. That may have been your intention, but I think something similar to how
Karn, Scion of Urza functions would have been cool here.
The flavor text doesn't feel very distinctive, which feels kind of like a miss.
I like this card a lot, but I think there were a few too many misses for it to pass on a 7-point totem.