Essentially, they're the cards you play to stick it to the man, or...you know, whatever
While its a great card, it shines best in Kindred decks, and I wanted this list to focus more on general utility and standalone power
If Crystal Barricade and other creatures you control would be dealt noncombat damage at the same time, the damage that would be dealt to your other creatures is prevented even if the damage being dealt to Crystal Barricade is lethal damage
The Keeper, when combined with Reds oath, Oath of Mages, kept you ahead of the curve
It was an interesting time for Arena, especially with Jumpstart: Historic Horizons
Perhaps it's an additive thing and Kastral used up many of the copies in circulation, allowing Keeper to spike now