While Zapdos isn't the most expensive Rocket card in Gym Challenge, it eclipses Giovanni and his iconic Gyarados
If another permanent becomes a copy of Court of Vantress, it will become a copy of whatever Court of Vantress is currently copying (if anything) that also has Court of Vantress's last ability
For a spoiler blog, this source supports the factual sections of the post
The Grixis color combination isn't great at ramping mana, but vampires tend to be very efficient in their cost and rely on each other for benefit, besides, you are limited to casting one collected card on each player's turn, so it's not broken right
Senseis Divining Top lets you draw the tutored card immediately, while Necropotence turns that precision into raw inevitability
The same goes for Thing in the Ice, where counter removal flips it into a massive board wipe threat ahead of schedule