It's a uniquely punishing effect that looks tailor-made for some of Commander's more ruthless leaders, and it's only been printed a couple of times, so Price of Glory earns its spot as one of the few cards in Odyssey worth more than $10
While Un-sets (like Unglued, Unhinged, Unstable, Unsanctioned, and Unfinity) are playable Magic cards, they exist outside the typical tournament legality and feature whimsical, often rule-bending mechanics
Apart from this article, I dont know anything about playtesting in Pokmon, especially not during the WotC era
Although there are only a few top level Rebels, there are enough Rebels that have a recruit ability and act like tutors to consistently fetch those into play
I have yet to see it be used in a really powerful way and is mostly a way to get out a chump after casting Koth when you are already behind