Well, you'll either need to collect the cards from Arena booster packs for the sets they came in, or else directly 'craft' the specific cards you need using MTG Arena Wildcards - effectively tokens you can exchange for the exact Common, Uncommon, Rare, or Mythic Rare card you want, depending on the type of Wildcard
Terra gains flying until the end of turn
And extra especially with utility discard
The set is a massive crossover that was five years in the making, and with over 100 legendary heroes and villains to choose from, picking a commander can feel like choosing your starting party for the first time
Of course, if your creatures power is lower than its toughness that's great, but if the creature you choose is indestructible you dont have to deal with that downside
The trade for this is that when he does quest for that impressive amount of lore, you can ready everything in your inkwell, letting you take, essentially, two rounds in one go