I wish this card saw more play, but I understand it's not exactly the most fun thing to be casting
Like most Magic: The Gathering cards, the value of Adarkar Sentinel depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Ice Age)
Setting these stops the XYZ summon from happening and removes access to the monster for the rest of the turn
Perhaps Whatnots greatest asset is its army of amateur auctioneers, who broadcast on their own channels, livestreaming sessions that can feature dozens of lots, each lasting a matter of seconds
The reprint of the Zendikar enemy-color fetch lands is a huge boost to this set, not to mention the introduction of Modern staples like Ragavan, Nimble Pilferer and the cycle of elementals