If you know a lot about your cards, youll have a better chance of securing a good price
What makes them good is that they deal with most of the problems you might face, be that a Baneslayer Angel, a Sword of Fire and Ice or a Moat (well, not Abrupt Decay but you get the point)
They were scared of his ability turning Standard into an interminable grind, and to be fair I can certainly imagine an alternate universe where that happened
Things can get a lot more complicated when different card types get onto the game zone like Enchantments, instant and Artifact cards
BT12-112 SEC Digimon Lv.7 Shoutmon X7: Superior Mode Color White Red Cost 15 DP 17000 Form Mega Attribute Data Type Composite/Xros Heart/Blue Flare Card Text 1 [Effect] When you would play this card, by placing 1 [Shoutmon] from play as a digivolution card of this Digimon, reduce the play cost by 1 and you may place cards in your trash as digivolution cards for a DigiXros
What Pokmon can compete with that