As a planeswalker, Tezzeret, Agent of Bolas acts like another player on your side of the battlefield, capable of activating one of its abilities each turn so long as you can pay the cost in the form of loyalty counters
While there are plenty of spells that can give negative stats to your opponents, Kaervek is great since it's a permanent ability, meaning unless either Maha or Kaervek gets removed, your opponents will be locked out of creatures
I also really like the way that this card plays in graveyard decks that include Bone Miser and other other enablers
If you enjoyed the Grimmsnarl VMAX from Darkness Ablaze, then this version will justify the price tag, which isn't even that high considering the potential cost that VMAX cards come with
(It must be noted that the actual sequence may be using two or more stacks of cards of the same rarity, e.g
Wouldnt you rather have a bunch of 4/4 Angels with flying and vigilance