One thing is certain – these types of cards are really successful in Commander and Casual circles.
In recent Magic history, similar cards have become near “auto include” for players during deckbuilding if they support the colors to do so. Here’s a few for reference:
In addition to library manipulation, Vizier of the Menagerie also provides extremely potent color fixing. That includes the ability to cast colorless creatures such as Reality Smasher. This is a lot of value, and rightly so for a mythic. I’m confidant this will be adopted quickly into existing Commander decks that play the color green (which is a lot). However, it remains to be seen if it can squeeze into a few slots into Constructed decks. The effects are powerful – but there may have to be a shift to a Midrange style of play for the Vizier to thrive.
I envision it could be played in a heavy creature list relying on creature density and can encorperate additional colors because of the fixing. Jund/RG/Temur color combinations instantly come to mind. All of these offer fantastic selection of creatures ranging across all the sets of Standard. A few I would love to play are Woodland Wanderer, Tireless Tracker, and the new card Glorybringer from Amonkhet.
There is a decent precedent to these types of cards proving themselves Constructed viable, since Oracle of Mul Daya was a key engine card when Primeval Titan, and Valakut of the Molten Pinnacle were wreaking havoc on Standard.
We’ll have to continue monitoring this card moving forward, but there’s already some clear signs of desire from players looking to acquire this card early on. We’ve seen values shift from when large stores starting opening pre-orders for Amonkhet, until now. I do think the best course of action is to wait, but I feel there was a good opportunity early on to secure one for playing purposes. With this recent value shift it wouldn’t be in a player’s best interest since that could change again drastically when Amonkhet is finally released officially.