Despite how long defender has been around, there aren't a ton of cards with defender in the game compared to other mechanics of its age, largely due to the pool of defenders being kept purposefully small as, by their nature, they have much less use than other mechanics outside of Limited formats
As such, if your child is younger than 13 but is already enjoying Magic: The Gathering at the local hobby shop with your permission, then theres nothing in MTG Arena that they arent already experiencing with the physical card game
The classic land destruction card is banned in all Constructed formats except Vintage and Legacy, and in Commander this is a particularly hated game-changer
Taking out Zetalpa, Primal Dawn is a pretty obvious choice since the card does nothing to further the strategy of your deck
When it comes to the most expensive Magic cards, the Power Nine are kings