The only other cards besides Zhulodok described as Legendary Creature - Eldrazi are the three titans and two Eldritch Moon cards - Brisela, Voice of Nightmares and Hanweir, Writhing Township
Sower of Discord Another Commander card designed for multiplayer formats because it can affect multiple players (which you probably want to be your opponents)
That said, MTG isnt very nice with 5-mana creatures that your opponents can kill cleanly, and by the time you can pay 7 mana to make it indestructible, they can have bounce or Inevitable Defeat
This seems to provide some quick delineation of which cards are affected and which aren't that's relatively simple to implement in a game with lots of numbers
Unreasonable, I don't care how many of these you jam into a deck
One-mana artifacts are already premium thanks to cards like Urza's Saga, but this is just a great artifact to have floating around