Quote from BlazingRagnarok »
Renzala, Crystal Gazer, even as far as high-risk, high-reward effects go, looks nigh-impossible to use. I guess it can limit the number of creatures your opponent playing in 1v1, but there's no way to use it in multiplayer. Not only does it have to survive two whole turns to do anything, but its ability can be disrupted by almost anything.
I believe that while it isn't as good as it would be in 1 v 1, there are many applications in multiplayer.
You can guess the number zero and then use an Evacuation effect at the end of your opponent's turn (right before your turn).
You can guess a number that is 1 or 2 higher than the number of creatures in play to discourage your opponent from playing additional creatures.
You can use mana efficient temporary removal spells (i.e. Snap, Submerge, Vapor Snag) to keep control of the number of creatures in play.
The card is interesting because even if you don't get to draw 3 cards because you still will most likely influence how your opponents decide to play or remove creatures. Additionally creatures with flash are good with Renzala, Crystal Gazer if the number you guessed was too low.