Youll need to control three permanents from other players to unlock Arvinox as a creature, which you can do by reanimating creatures from their graveyards, using the ability of cards like Gonti, Lord of Luxury, or with Arvinoxs own ability
The set included Robin Hood, Captain Hook, Stitch, Cruella De Vil, Elsa and Mickey Mouse cards, along with two commemorative pins - its not yet clear if these same card versions will eventually appear in Lorcanas first main set
If you have a deck that runs Overwhelming Stampede or Overrun, consider this instead
The existing decks that will probably include Karn in their 75 are GB Constrictor, Mardu Vehicles, and Grixis/UB Improvise
It's a tokens deck
Youre going to attack anyway, and this keeps up a steady stream of bodies