In reality, Pocket is a game of chance and there is no sinister plot behind the scenes to overflow trainers' collections with Onix
Sorcerer Enchanted creature gets +1/+1 and has "Whenever this creature attacks, scry 1." Wicked Enchanted creature gets +1/+1 and "When this Aura is put into a graveyard from the battlefield, each opponent loses 1 life." Young Hero Enchanted creature has "Whenever this creature attacks, if its toughness is 3 or less, put a +1/+1 counter on it." Any time a creature has more than one Role controlled by the same player attached to it, the creature keeps the newest Role and all the others controlled by that player are put into the graveyard (and then cease to exist because they're tokens)
The card is iconic, cool, actually playable (and goes infinite with Mana Echoes), and is worth a pretty penny
Getting a free Shock every time one of your Dragons, itself included, attacks is a huge deal
Metalmorph X TRAP Target 1 face-up monster on the field
Mummy has high attack so you can win faster and more easily facilitates the Alucard lock down