Given that Vivi Ornitier was banned in Magic: the Gathering's Standard format more than a month ago, you may have thought that you had seen the last of the small but mighty spellcaster
Pawniard 132/198 Loading
Then she has the -2 to exile any enchantment, tapped creature, or artifact
While there are guidelines to keep in mind when deck building (no Game Changers in Exhibition or Core, no mass land denial through Upgraded, etc.), the bracket system is emphatically not just "put your deck into a calculator, get assigned a rank, and be ready to play." I deeply appreciate the tools that websites like Moxfield and Archidekt have put together to give you an overall estimate, and they've done some fantastic iteration to help emphasize intent as wellbut I want to stress that any estimate is just an estimate
Scale Up
Since I'm not convinced Invasion of Tarkir is worth playing outside of a Dragon deck and there aren't currently any top-tier Dragon decks, I'm going to put it in B-tier, although the card should be very, very good in a Dragon deck