Presumably, he's not playing a deck with Black or White cards, huh
To gather all of the cards from a set, you can purchase them in smaller packs called booster packs or purchase products with a selection of specific cards.
I'm NOT providing card-for-card swaps for these, but the general rule of thumb is take out cards that fulfill the same role but worse: take out a land for a land, removal for removal, card draw for card draw, etc
(Every set, we ask Magic -playing employees to give us their first impressions of the cards.) The development team decided to take the best one (the green one), make it bigger, give it trample to help it get through, and then scrap the other four
Being able to play it as a creature board wipe in the late game when you don't need more lands is awesome, provided that you have a legendary artifact on hand to sacrifice