The spells you're going to want the most are what are called "removal spells"these are the spells that permanently neutralize your opponent's creatures by either dealing damage, keeping them tapped, or just straight-up destroying them
Thoughtseize is the most powerful of the family, casting a shadow over all other options
Green is the best individual color in the color pie at performing this task, as it provides ample ways to put extra lands onto the battlefield from your hand or deck as well as efficient ways to add extra mana to your mana pool via creatures, enchantments, and artifacts
A card that transforms but is also a copy of something, remains a copy of what it was before, even though it does change which face is turned up on the playing surface
Searching up cards like Daybreak Coronet, Spirit Mantle, and Ethereal Armor will make Zur more and more powerful, and he will quickly become a virtually untouchable enchanted monster capable of one-shotting other players with commander damage