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
On the other hand, if the table went on a Collective Voyage with you at the beginning of the game, they are going to be suffering rather painfully under the enchantment
So if you build your deck with this in mind there is a hidden draw a card on Onslaught
He delivers steady card advantage and token replacement, which makes Zombie decks smoother and more forgiving across long games
If the creatures are too much to handle, it's good to use the creature destruction effect, and if the battlefield is manageable, destroying all lands is the way to go
In every game, youre fighting against the random card draw mechanics to pull the most important creatures from your deck