When you can play it the Cloud brings awesome power offering a pretty good representation of a Mind Twist, an Armageddon, a Wrath of God or a Fireball, often a couple of those things and almost always far worse for your opponent than you
Between 1,000 and 5,000, or greater than that, like card shop levels
Your Grafidggers Cage or Nihil Spellbomb look a lot scarier when you have a Tarmogoyf in play because I am forced to piece something together in a couple turns as opposed to ten
As handsome as Astarion might be, people seem to have just had their fill
But even without all the support backing up Rampaging Ferocidon, it on its own can shut down a lot of plays
Cards in this category offer a natural play pattern of just plotting the cards if you have extra mana to do so on a given turn, or casting them as normal on turns when you can otherwise afford to do so