It's done by preventing a dominant strategy from emerging
After the printing of cards cards like Icatian Lieutenant, Dwarven Soldier, and Goblin Chirurgeon in the Fallen Empires set, players realized that there was another factor that mattered besides the color of the card and the mana cost
Enchantment Violent Outburst Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less
Looking for grades is a good way to make sure you get cards that are truly valuable
Considering how terrifying this Pokemon's lore is, we could imagine some concept cards being scrapped for being a bit too over-the-top and horrifying to fit in with the more kid-friendly options
Xenagos, the Reveler : Im not entirely sure he deserves a spot in the deck, but Im hoping he does good work